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_______________________________________________________________ maxim integrated products 1 for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxims website at www.maxim-ic.com. multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A general description the max17126/MAX17126A generate all the supply rails for thin-film transistor liquid-crystal display (tft lcd) tv panels operating from a regulated 12v input. they include a step-down and a step-up regulator, a positive and a negative charge pump, an operational amplifier, a high-accuracy high-voltage gamma reference, and a high-voltage switch control block. the max17126/ MAX17126A can operate from input voltages from 8v to 16.5v and is optimized for an lcd tv panel running directly from 12v supplies. the step-up and step-down switching regulators feature internal power mosfets and high-frequency opera - tion allowing the use of small inductors and capacitors, resulting in a compact solution. the step-up regulator provides tft source driver supply voltage, while the step-down regulator provides the system with logic sup - ply voltage. both regulators use fixed-frequency current- mode control architectures, providing fast load-transient response and easy compensation. a current-limit func - tion for internal switches and output-fault shutdown pro - tects the step-up and step-down power supplies against fault conditions. the max17126 /MAX17126A provide soft-start functions to limit inrush current during startup. in addition, the max17126 /MAX17126A integrate a con- trol block that can drive an external p-channel mosfet to sequence power to source drivers. the positive and negative charge-pump regulators pro - vide tft gate-driver supply voltages. both output volt - ages can be adjusted with external resistive voltage- dividers. a logic-controlled, high-voltage switch block allows the manipulation of the positive gate-driver supply. the max17126/MAX17126A include one high-current operational amplifier designed to drive the lcd back - plane (vcom). the amplifier features high output cur - rent ( q 200ma), fast slew rate (45v/f s), wide bandwidth (20mhz), and rail-to-rail outputs. also featured in the max17126/ MAX17126A is a high- accuracy, high-voltage adjustable reference for gamma correction. the max17126 /MAX17126A are available in a small (7mm x 7mm), ultra-thin (0.8mm), 48-pin thin qfn package and operate over the -40 n c to +85n c temperature range. applications lcd tv panels features s 8.0v to 16.5v in supply-voltage range s selectable frequency (500khz/750khz) s current-mode step-up regulator fast load-transient response high-accuracy output voltage (1.0%) built-in 20v, 4.2a, 100m i mosfet high efficiency adjustable soft-start adjustable current limit low duty-cycle operation (13.2v in - 13.5v avdd) s current-mode step-down regulator fast load-transient response built-in 20v, 3.2a, 100m i mosfet high efficiency 3ms internal soft-start s adjustable positive charge-pump regulator s adjustable negative charge-pump regulator s integrated high-voltage switch with adjustable turn-on delay s high-speed operational amplifier q 200ma short-circuit current 45v/s slew rate s high-accuracy reference for gamma buffer q1% feedback voltage up to 30ma load current low-dropout voltage 0.5v at 60ma s external p-channel gate control for avdd sequencing s pgood comparator s input undervoltage lockout and thermal- overload protection s 48-pin, 7mm x 7mm, thin qfn package 19-4681; rev 1; 3/10 pin configuration appears at end of data sheet. + denotes a lead(pb)-free/rohs-compliant package. * ep = exposed pad. ordering information evaluation kit available part temp range pin-package max17126etm+ -40n c to +85nc 48 thin qfn-ep* MAX17126Aetm+ -40n c to +85nc 48 thin qfn-ep* www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A 2 ______________________________________________________________________________________ stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. these are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. invl, in2, vop, en, fsel to gnd ....................... -0.3v to +24v pgnd, ognd, cpgnd to gnd .......................... -0.3v to +0.3v dly1, gvoff, thr, vl to gnd .......................... -0.3v to +7.5v ref, fbp, fbn, fb1, fb2, comp, ss, clim, pgood, vdet, vref_fb, out to gnd ....... .-0.3v, (v l + 0.3) gd, gd_i to gnd .................................................. -0.3v to +24v lx1 to pgnd ......................................................... -0.3v to +24v opp, opn, opo to ognd ......................... -0.3v to vop + 0.3v drvp to cpgnd ...................................... -0.3v to supp + 0.3v drvn to cpgnd ...................................... -0.3v to supn + 0.3v lx2 to pgnd ................................................ -0.7 to (in2 + 0.3v) supn to gnd ............................................. -0.3v to (in2 + 0.3v) supp to gnd .......................................... -0.3v to (gd_i + 0.3v) bst to vl ............................................................... -0.3v to +30v vgh to gnd .......................................................... -0.3v to +40v vghm, drn to gnd ..................................... -0.3v, vgh + 0.3v vghm to drn ....................................................... -0.3v to +40v vref_i to gnd ...................................................... -0.3v to +24v vref_o to gnd ....................................... -0.3v, (v ref_i + 0.3)v ref short circuit to gnd .......................................... continuous rms lx1 current (total for both pins) ................................. 3.2 a rms pgnd current (total for both pins) ........................ 3.2 a rms in2 current (total for both pins) ................................. 3.2 a rms lx2 current (total for both pins) ................................. 3.2 a rms drvn, drvp current .................................................. 0.8a rms vl current .................................................................. 50ma continuous power dissipation (t a = +70nc) 48-pin tqfn (derated 38.5mw/ n c above +70nc) ....................... 3076.9mw junction temperature ..................................................... +160nc storage temperature range ............................ -65n c to +165nc lead temperature (soldering, 10s) ................................ +300nc soldering temperature (reflow) ...................................... +260nc electrical characteristics (circuit of figure 1, v invl = v in2 = 12v, v vop = v vref_i = 15v, t a = 0 c to +85c . typical values are at t a = +25 n c, unless oth- erwise noted.) absolute maximum ratings parameter conditions min typ max units general invl, in2 input-voltage range 8 16.5 v invl + in2 quiescent current only lx2 switching (v fb1 = v fbp = 1.5v, v fbn = 0v) en = vl, fsel = high 8.5 20 ma invl + in2 standby current lx2 not switching (v fb1 = v fb2 = v fbp = 1.5v, v fbn = 0v), en = vl, fsel = high 24 5 ma smps operating frequency fsel = invl or high impedance 630 750 870 khz fsel = gnd 420 500 580 invl undervoltage-lockout threshold invl rising, 150mv typical hysteresis 6.0 7.0 8.0 v vl regulator vl output voltage i vl = 25ma, v fb1 = v fb2 = v fbp = 1.1v, v fbn = 0.4v (all regulators switching) 4.85 5 5.15 v vl undervoltage-lockout threshold vl rising, 50mv typical hysteresis 3.5 3.9 4.3 v reference ref output voltage no external load 1.2375 1.250 1.2625 v ref load regulation 0v < i load < 50 fa 5 mv ref sink current in regulation 10 fa ref undervoltage-lockout threshold rising edge, 250mv typical hysteresis 1.0 1.2 v www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A _______________________________________________________________________________________ 3 electrical characteristics (continued) (circuit of figure 1, v invl = v in2 = 12v, v vop = v vref_i = 15v, t a = 0 c to +85c . typical values are at t a = +25 n c, unless oth- erwise noted.) dual mode is a trademark of maxim integrated products, inc. parameter conditions min typ max units step-down regulator out voltage in fixed mode fb2 = gnd, no load (note 1) 0c < t a = +85c 3.25 3.3 3.35 v t a = +25c 3.267 3.333 fb2 voltage in adjustable mode v out = 2.5v, no load (note 1) 0c < t a = +85c 1.23 1.25 1.27 v t a = +25c 1.2375 1.2625 fb2 adjustable mode threshold voltage dual mode? comparator 0.10 0.15 0.20 v output voltage adjust range 1.5 5 v fb2 fault-trip level falling edge 0.96 1.0 1.04 v fb2 input leakage current v fb2 = 1.25v 50 125 200 na dc load regulation 0v < i load < 2a 0.5 % dc line regulation no load, 10.8v < v in2 < 13.2v 0.1 %/v lx2-to-in2 nmos switch on-resistance 100 200 mi lx2-to-gnd2 nmos switch on-resistance 6 10 23 i bst-to-vl pmos switch on-resistance 40 30 110 i low-frequency operation out threshold lx2 only 0.8 v low-frequency operation switching frequency fsel = invl 125 khz fsel = gnd 83 lx2 positive current limit max17126 2.50 3.20 3.90 a MAX17126A 3.0 3.5 4.0 soft-start ramp time zero to full limit 3 ms maximum duty factor 70 78 85 % minimum duty factor char/design limit only 10 % step-up regulator output voltage range vin 20 v oscillator maximum duty cycle 70 78 85 % fb1 regulation voltage fb1 = comp, c comp = 1nf 1.2375 1.25 1.2625 v fb1 fault trip level falling edge 0.96 1.0 1.04 v fb1 load regulation 0v < i load < full 0.5 % fb1 line regulation 10.8v < v in < 13.2v 0.08 %/v fb1 input bias current v fb1 = 1.25v 30 125 200 na fb1 transconductance d i = q2.5f a at comp, fb1 = comp 150 320 560 fs fb1 voltage gain fb1 to comp 1400 v/v lx1 leakage current v fb1 = 1.5v, v lx1 = 20v 10 40 fa www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A 4 ______________________________________________________________________________________ electrical characteristics (continued) (circuit of figure 1, v invl = v in2 = 12v, v vop = v vref_i = 15v, t a = 0 c to +85c . typical values are at t a = +25 n c, unless oth- erwise noted.) parameter conditions min typ max units lx1 current limit v fb1 = 1.1v, r clim = unconnected 3.6 4.2 4.8 a v fb1 = 1.1v, with r clim at clim pin -20% 4.2 - (68k/ r clim ) +20% clim voltage r clim = 60.5k i 0.56 0.625 0.69 v current-sense transresistance 0.19 0.21 0.25 v/a lx1 on-resistance 100 185 mi soft-start period c ss < 200pf 16 ms ss charge current v ss = 1.2v 4 5 6 fa positive charge-pump regulators gd_i input supply range 8.0 20 v gd_i input supply current v fbp = 1.5v (not switching) 0.15 0.3 ma gd_i overvoltage threshold gd_i rising, 250mv typical hysteresis (note 2) 20.1 21 22 v fbp regulation voltage 1.2375 1.25 1.2625 v fbp line regulation error v sup = 11v to 16v, not in dropout 0.2 %/v fbp input bias current v fbp = 1.5v, t a = +25c -50 +50 na drvp p-channel mosfet on-resistance 1.5 3 i drvp n-channel mosfet on-resistance 1 2 i fbp fault trip level falling edge 0.96 1.0 1.04 v positive charge-pump soft-start period 7-bit voltage ramp with filtering to prevent high peak currents 500khz frequency 4 ms 750khz frequency 3 ms negative charge-pump regulators fbn regulation voltage v ref - v fbn 0.99 1.00 1.01 v fbn input bias current v fbn = 0mv, t a = +25c -50 +50 na fbn line regulation error v in2 = 11v to 16v, not in dropout 0.2 %/v drvn p ch on-resistance 1.5 3 i drvn n ch on-resistance 1 2 i fbn fault trip level rising edge 720 800 880 mv negative charge-pump soft- start period 7-bit voltage ramp with filtering to prevent high peak currents 500khz frequency 3 ms 750khz frequency 2 avdd switch gate control gd to gd_i pullup resistance en = gnd 25 50 i gd output sink current en = vl 5 10 15 fa gd done threshold en = vl, v gd_i - v gd 5 6 7 v operational amplifiers vop supply range 8 20 v www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A _______________________________________________________________________________________ 5 electrical characteristics (continued) (circuit of figure 1, v invl = v in2 = 12v, v vop = v vref_i = 15v, t a = 0 c to +85c . typical values are at t a = +25 n c, unless oth- erwise noted.) parameter conditions min typ max units vop overvoltage fault threshold v vop = rising, hysteresis = 200mv (note 2) 20.1 21 22 v vop supply current buffer configuration, v opp = v opn = vop/2, no load 2 4 ma input offset voltage 2v < (v opp , v opn ) < (v vop - 2v) 3 14 mv input bias current 2v < (v opp , v opn ) < (v vop - 2v) -1 +1 fa input common-mode voltage range 0 vop v input common-mode rejection ratio 2v < (v opp , v opn ) < (v vop - 2v) 80 db output voltage swing high i opo = 25ma vop - 320 vop - 150 mv output voltage swing low i opo = -25ma 150 300 mv large-signal voltage gain 2v < (v opp , v opn ) < (v op - 2v) 80 db slew rate 2v < (v opp , v opn ) < (v op - 2v) 45 v/fs -3db bandwidth 2v < (v opp , v opn ) < (v op - 2v) 20 mhz short-circuit current short to v vop /2, sourcing 200 ma short to v vop /2, sinking 200 high-voltage switch array vgh supply range 35 v vgh supply current 150 300 fa vghm-to-vgh switch on-resistance v dly1 = 2v, gvoff = vl 5 10 i vghm-to-vgh switch saturation current v vgh - v vghm > 5v 150 390 ma vghm-to-drn switch on-resistance v dly1 = 2v, gvoff = gnd 20 50 i vghm-to-drn switch saturation current v vghm - v drn > 5v 75 200 ma vghm-to-gnd switch on-resistance dly1 = gnd 1.0 2.5 4.0 ki gvoff input low voltage 0.6 v gvoff input high voltage 1.6 v gvoff input current v gvoff = 0v or vl, t a = +25c -1 +1 fa gvoff-to-vghm rising propagation delay 1ki from drn to cpgnd, v gvoff = 0v to vl step, no load on vghm, measured from gvoff = 2v to vghm = 20% 100 ns gvoff-to-vghm falling propagation delay 1k i from drn to cpgnd, v gvoff = vl to 0v step, no load on vghm, drn falling, no load on drn and vghm, measured from v gvoff = 0.6v to vghm = 80% 200 ns thr-to-vghm voltage gain 9.4 10 10.6 v/v www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A 6 ______________________________________________________________________________________ electrical characteristics (continued) (circuit of figure 1, v invl = v in2 = 12v, v vop = v vref_i = 15v, t a = 0 c to +85c . typical values are at t a = +25 n c, unless oth- erwise noted.) parameter conditions min typ max units sequence control en pulldown resistance 1 mi dly1 charge current v dly1 = 1v; when dly1 cap is not used, there is no delay 6 8 10 fa en, dly1 turn-on threshold 1.19 1.25 1.31 v dly1 discharge switch on-resistance en = gnd or fault tripped 10 i fbn discharge switch on-resistance (en = gnd and invl < uvlo) or fault tripped 3 ki gamma reference vref_i input-voltage range 10 18.0 v vref_i input bias current no load 125 250 fa vref_o dropout voltage i vref_o = 60ma 0.25 0.5 v vref_fb regulation voltage v vref_i = 13.5v, 1ma p i vref_o p 30ma, v vref_o = 9.5v 1.243 1.250 1.256 v v vref_i from 10v to 18v, i vref_o = 20ma, v vref_o = 9.5v p 0.9 mv/v vref_o maximum output current 60 ma pgood function vdet threshold vdet rising 1.274 1.3 1.326 v vdet hysteresis 50 mv vdet input bias current 50 175 300 na pgood output voltage vdet = agnd, i pgood = 1ma 0.4 v fault detection duration-to-trigger fault for uvp only 50 ms step-up short-circuit protection fb1 falling edge 0.36 x v ref 0.4 x v ref 0.44 x v ref v step-down short-circuit protection adjustable mode fb2 falling 0.18 x v ref 0.2 x v ref 0.22 x v ref v fixed mode out falling, internal feedback divider voltage 0.18 x v ref 0.2 x v ref 0.22 x v ref positive charge-pump short-circuit protection fbp falling edge 0.36 x v ref 0.4 x v ref 0.44 x v ref v negative charge-pump short-circuit protection v ref - v fbn 0.4 0.45 0.5 v thermal-shutdown threshold latch protection +160 nc www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A _______________________________________________________________________________________ 7 electrical characteristics (v invl = v in2 = 12v, v vop = v vref_i = 15v, t a = -40 n c to +85nc .) (note 3) electrical characteristics (continued) (circuit of figure 1, v invl = v in2 = 12v, v vop = v vref_i = 15v, t a = 0 c to +85c . typical values are at t a = +25 n c, unless oth- erwise noted.) parameter conditions min typ max units switching frequency selection fsel input low voltage 500khz 0.6 v fsel input high voltage 750khz 1.6 v fsel pullup resistance 1 mi parameter conditions min typ max units general invl, in2 input-voltage range 8 16.5 v smps operating frequency fsel = invl or high impedance 630 870 khz fsel = gnd 420 580 invl undervoltage-lockout threshold invl rising, 150mv typical hysteresis 6.0 8.0 v vl regulator vl output voltage i vl = 25ma, v fb1 = v fb2 = v fb = 1.1v, v fbn = 0.4v (all regulators switching) 4.85 5.15 v vl undervoltage-lockout threshold vl rising, 50mv typical hysteresis 3.5 4.3 v reference ref output voltage no external load 1.235 1.265 v ref undervoltage-lockout threshold rising edge, 25mv typical hysteresis 1.2 v step-down regulator out voltage in fixed mode fb2 = gnd, no load (note 1) 3.267 3.333 v fb2 voltage in adjustable mode v out = 2.5v, no load (note 1) 1.2375 1.2625 v fb2 adjustable mode threshold voltage dual-mode comparator 0.10 0.20 v output voltage adjust range 1.5 5 v fb2 fault trip level falling edge 0.96 1.04 v lx2-to-in2 nmos switch on-resistance 200 mi lx2-to-gnd2 nmos switch on-resistance 6 23 i bst-to-vl pmos switch on-resistance 40 110 i lx2 positive current limit max17126 2.50 3.90 a MAX17126A 3.0 4.0 maximum duty factor 70 85 % www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A 8 ______________________________________________________________________________________ electrical characteristics (continued) (v invl = v in2 = 12v, v vop = v vref_i = 15v, t a = -40 n c to +85nc .) (note 3) parameter conditions min typ max units step-up regulator output-voltage range vin 20 v oscillator maximum duty cycle 70 85 % fb1 regulation voltage fb1 = comp, c comp = 1nf 1.2375 1.2625 v fb1 fault trip level falling edge 0.96 1.04 v fb1 transconductance d i = q2.5f a at comp, fb1 = comp 150 560 fs lx1 input bias current v fb1 = 1.5v, v lx1 = 20v 40 fa lx1 current limit v fb1 = 1.1v, r clim = unconnected 3.6 4.8 a v fb1 = 1.1v , with r clim at clim pin, limit = 3.5a - (60.5k/r clim ) -20% +20% clim voltage r clim = 60.5k i 0.56 0.69 v current-sense transresistance 0.19 0.25 v/a lx1 on-resistance 185 mi ss charge current v ss = 1.2v 4 6 fa positive charge-pump regulators gd_i input supply range 8.0 20 v gd_i input supply current v fbp = 1.5v (not switching) 0.2 ma gd_i overvoltage threshold gd_i rising, 250mv typical hysteresis (note 2) 20.1 22 v fbp regulation voltage 1.243 1.256 v fbp line regulation error v sup = 11v to 16v, not in dropout 0.2 %/v drvp p-channel mosfet on-resistance 3 i drvp n-channel mosfet on-resistance 1 i fbp fault trip level falling edge 0.96 1.04 v negative charge-pump regulators fbn regulation voltage v ref - v fbn 0.99 1.01 v fbn line regulation error v in2 = 11v to 16v, not in dropout 0.2 %/v drvn p ch on-resistance 3 i drvn n ch on-resistance 1 i fbn fault trip level rising edge 720 880 mv avdd switch gate control gd output sink current en = vl 5 15 fa gd done threshold en = vl, vgd_i - vgd 5 7 v www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A _______________________________________________________________________________________ 9 electrical characteristics (continued) (v invl = v in2 = 12v, v vop = v vref_i = 15v, t a = -40 n c to +85nc .) (note 3) parameter conditions min typ max units operational amplifiers vop supply range 8 20 v vop overvoltage fault threshold v op = rising, hysteresis = 200mv (note 2) 20.1 22 v vop supply current buffer configuration, v opp = v opn = v op /2, no load 4 ma input offset voltage 2v < (v opp , v opn ) < (v op - 2v) 14 mv input common-mode voltage range 0 ovin v output voltage swing high i opo = 25ma vop - 320 mv output voltage swing low i opo = -25ma 300 mv short-circuit current short to v opo /2, sourcing 200 ma short to v opo /2, sinking 200 high-voltage switch array vgh supply range 35 v vgh supply current 300 fa vghm-to-vgh switch on-resistance v dly1 = 2v, gvoff = vl 10 i vghm-to-vgh switch saturation current v vgh - v vghm > 5v 150 ma vghm-to-drn switch on-resistance v dly1 = 2v, gvoff = gnd 50 i vghm-to-drn switch saturation current v vghm - v drn > 5v 75 ma vghm-to-gnd switch on-resistance dly1 = gnd 1.0 4.0 ki gvoff input low voltage 0.6 v gvoff input high voltage 1.6 v thr-to-vghm voltage gain 9.4 10.6 v/v sequence control en input low voltage 0.6 v en input high voltage 1.6 v dly1 charge current v dly1 = 1v; when dly1 cap is not used, there is no delay 6 10 fa dly1 turn-on threshold 1.19 1.31 v www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A 10 _____________________________________________________________________________________ electrical characteristics (continued) (v invl = v in2 = 12v, v vop = v vref_i = 15v, t a = -40 n c to +85nc .) (note 3) note 1: when the step-down inductor is in continuous conduction (en = vl or heavy load), the output voltage has a dc regulation level lower than the error comparator threshold by 50% of the output voltage ripple. in discontinuous conduction (en = gnd with light load), the output voltage has a dc regulation level higher than the error comparator threshold by 50% of the output voltage ripple. note 2: disables boost switching if either gd_i or vop exceeds the threshold. switching resumes when no threshold is exceeded. note 3: specifications to t a = -40 n c are guaranteed by design, not production tested. parameter conditions min typ max units gamma reference vref_i input voltage range 10 18.0 v vref_i undervoltage lockout vref_i rising 5.2 v vref_i input bias current no load 250 fa vref_o dropout voltage i vref_o = 60ma 0.5 v vref_fb regulation voltage v ref_i = 13.5v, 1ma i vref_o 30ma 1.2375 1.2625 v v ref_i from 10v to 18v, i vref_o = 20ma p 0.9 mv/v vref_o maximum output current 60 ma pgood function vdet threshold vdet rising 1.274 1.326 v pgood output voltage vdet = agnd, i pgood = 1ma 0.4 v fault detection step-up short-circuit protection fb1 falling edge 0.36 x v ref 0.44 x v ref v step-down short-circuit protection adjustable mode fb2 falling 0.18 x v ref 0.22 x v ref v fixed mode out falling, internal feedback divider voltage 0.18 x v ref 0.22 x v ref v positive charge-pump short-circuit protection fbp falling edge 0.36 x v ref 0.44 x v ref v negative charge-pump short-circuit protection v ref - v fbn 0.4 0.5 v switching frequency selection fsel input low voltage 500khz 0.6 v fsel input high voltage 750khz 1.6 v www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A ______________________________________________________________________________________ 11 typical operating characteristics (t a = +25c, unless otherwise noted.) step-down regulator efficiency vs. load current max17126 toc01 load current (a) efficiency (%) 1.00 55 60 65 70 75 80 85 50 0.10 10.00 750khz 500khz step-down regulator output voltage vs. load current max17126 toc02 load current (a) output voltage (v) 2.00 1.60 1.20 0.80 0.42 3.300 3.325 3.350 3.275 0 2.40 750khz 500khz step-up regulator efficiency vs. load current max17126 toc05 load current (a) efficiency (%) 1.00 0.10 55 60 65 70 75 80 85 90 95 100 50 0.01 10.00 750khz 500khz step-up regulator output voltage vs. load current max17126 toc06 load current (a) output voltage (v) 2.0 1.5 1.0 0.5 16.415 16.420 16.425 16.430 16.435 16.440 16.445 16.410 0 2.5 750khz 500khz step-down regulator load transient response (0.3a to 1.8a) max17126 toc03 v out (ac-coupled) 200mv/div 0v 0a 0a i l2 1a/div i load 1a/div 20fs/div l = 4.7fh step-down regulator heavy-load soft-start (1a) max17126 toc04 v in 5v/div v out 1v/div 0v 0v 0a 0a i l2 1a/div lx2 10v/div 4ms/div www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A 12 _____________________________________________________________________________________ typical operating characteristics (continued) (t a = +25c, unless otherwise noted.) switching frequency vs. input voltage max17126 toc10 v in (v) switching frequency (khz) 14 12 10 489 490 491 492 493 494 495 496 497 498 488 8 16 gamma reference line regulation (load = 20ma) max17126 toc12 vop voltage (v) gamma reference voltage (v) 17.5 17.0 16.5 16.0 15.5 14.89 14.94 14.99 15.04 15.09 15.14 14.84 15.0 18.0 gamma reference load regulation (v ref = 16v) max17126 toc13 load current (ma) gamma reference voltage (v) 200 150 100 50 14.6 14.7 14.8 14.9 15.0 15.1 15.2 14.5 0 250 reference voltage load regulation max17126 toc11 load current (fa) reference voltage (v) 150 100 50 1.2470 1.2475 1.2480 1.2485 1.2490 1.2465 0 200 switching no switching step-up regulator pulsed load transient response (0.1a to 1.9ma) max17126 toc08 0v 0a 0a i l1 1a/div 10fs/div l = 10fh v avdd (ac-coupled) 200mv/div i load 1a/div step-up regulator heavy load soft-start (0.5a) max17126 toc09 0v 0v 0v 0a i l1 1a/div 1ms/div v avdd 5v/div v gd 5v/div en 5v/div step-up regulator load transient response (0.1a to 1.1a) max17126 toc07 0v 0a 0a i l1 1a/div 20fs/div l = 10fh v avdd (ac-coupled) 200mv/div i load 1a/div www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A ______________________________________________________________________________________ 13 typical operating characteristics (continued) (t a = +25c, unless otherwise noted.) positive charge-pump regulator normalized line regulation max17126 toc14 supp voltage (v) v gon error (%) 17 16 15 14 13 12 11 -10 -8 -6 -4 -2 0 2 -12 10 18 i gon = 0a i gon = 25ma positive charge-pump regulator normalized load regulation max17126 toc15 load current (ma) output current error (%) 100 50 -1.5 -1.0 -0.5 0 0.5 -2.0 0 150 positive charge-pump regulator load-transient response max17126 toc16 0v 0a i load 20ma/div 40fs/div v gon (ac-coupled) 200mv/div 60ma 10ma negative charge-pump regulator normalized line regulation max17126 toc17 supn voltage (v) v goff error (%) 15 14 13 12 11 10 9 -0.03 -0.02 -0.01 0 0.01 -0.04 8 16 i gon = 25ma i gon = 0ma negative charge-pump regulator normalized load regulation max17126 toc17 load current (ma) output voltage error (%) 250 200 150 100 50 -1.0 -0.8 -0.6 -0.4 -0.2 0 0.2 -1.2 0 300 negative charge-pump regulator load transient response max17126 toc19 0v 0a i load 20ma/div 20fs/div v goff (ac-coupled) 200mv/div 60ma 10ma www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A 14 _____________________________________________________________________________________ typical operating characteristics (continued) (t a = +25c, unless otherwise noted.) operational amplifier rail-to-rail input/output waveforms max17126 toc21 0v 0v 4fs/div v opp 5v/div v com 5v/div operational amplifier load transient response max17126 toc22 0v 0a 1fs/div v com (ac-coupled) 500mv/div i vcom 100ma/div op amp supply current vs. supply voltage max17126 toc20 vop voltage (v) vop supply current (ma) 19 18 17 16 15 14 13 12 11 10 9 2.35 2.40 2.45 2.50 2.55 2.60 2.65 2.30 8 20 power-up sequence of all supply outputs max17126 toc19 0v 0v 0v 0v 0v 0v 0v 0v 0v 10ms/div v in v out v goff v avdd v gon v com v dly1 v ghm v in = 10v/div v out = 5v/div v goff = 10v/div v avdd =10v/div v gon = 20v/div v com = 10v/div v dly1 = 5v/div v ghm = 50v/div www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A ______________________________________________________________________________________ 15 typical operating characteristics (continued) (t a = +25c, unless otherwise noted.) v in supply current vs. v in voltage max17126 toc26 input voltage (v) invl current ( m a) 14 12 10 1 2 3 4 5 6 7 0 8 16 all output switching no output switching buck output switching operational amplifier large-signal step response max17126 toc23 0v 0v 1fs/div v opp 5v/div v com 5v/div operational amplifier small-signal step response max17126 toc25 0v 0v 100ns/div v opp (ac-coupled) 200mv/div v com (ac-coupled) 200mv/div high-voltage switch control function (vghm with 470pf load) max17126 toc27 0v 0v 4fs/div v gvoff 5v/div v ghm 10v/div www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A 16 _____________________________________________________________________________________ pin description pin name function 1 vref_i gamma reference input 2 vop operational amplifier power supply 3 ognd operational amplifier power ground 4 opp operational amplifier noninverting input 5 opn operational amplifier inverting input 6 opo operational amplifier output 7 pgood input voltage power-good open-drain output pulled high to vl or 3.3v through 10k i resistor. 8 gvoff high-voltage switch-control block timing control input. see the high-voltage switch control section for details. 9 en enable input. enable is high, turns on step-up converter and positive charge pump. 10 fb2 step-down regulator feedback input. connect fb2 to gnd to select the step-down converters 3.3v fixed mode. for adjustable mode, connect fb2 to the center of a resistive voltage-divider between the step-down regulator output (out) and gnd to set the step-down regulator output voltage. place the resistive voltage-divider within 5mm of fb2. 11 out step-down regulator output voltage sense. connect out to step-down regulator output. 12 n.c. not connected 13, 14 lx2 step-down regulator switching node. lx2 is the source of the internal n-channel mosfet connected between in2 and lx2. connect the inductor and schottky catch diode to both lx2 pins and minimize the trace area for lowest emi. 15 bst step-down regulator bootstrap capacitor connection. power supply for high-side gate driver. connect a 0.1 f f ceramic capacitor from bst to lx2. 16, 17 in2 step-down regulator power input. drain of the internal n-channel mosfet connected between in2 and lx2. 18, 44 gnd analog ground 19 vdet voltage-detector input. connects vdet to the center of a resistor voltage-divider between input voltage and gnd to set the trigger point of pgood. 20 invl internal 5v linear regulator and the startup circuitry power supply. bypass v invl to gnd with 0.22 ff close to the ic. 21 vl 5v internal linear regulator output. bypass vl to gnd with 1 f f minimum. provides power for the internal mosfet driving circuit, the pwm controllers, charge-pump regulators, logic, and reference and other analog circuitry. provides 25ma load current when all switching regulators are enabled. vl is active whenever input voltage is high enough. 22 fsel frequency select pin. connect fsel to vl or invl or float fsel pin for 750khz operation. connect to gnd for 500khz operation. 23 clim boost current-limit setting input. connects a resistor from clim to gnd to set current limit for boost converter. 24 ss soft-start input. connects a capacitor from ss to gnd to set the soft-start time for the step-up convert - er. a 5 f a current source starts to charge c ss when gd is done. see the step-up regulator external pmos pass switch section for description. ss is internally pulled to gnd through 1k i resistance when en is low or when vl is below its uvlo threshold. 25, 26 lx1 step-up regulator power-mosfet n-channel drain and switching node. connects the inductor and schottky catch diode to both lx1 pins and minimizes the trace area for lowest emi. 27, 28 pgnd step-up regulator power ground 29 gd_i step-up regulator external pmos pass switch source input. connects to the cathode of the step-up regulator schottky catch diode. www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A ______________________________________________________________________________________ 17 pin description (continued) pin name function 30 gd step-up regulator external pmos pass switch gate input. a 10 fa p 20% current source pulls down on the gate of the external pfet when en is high. 31 fb1 boost regulator feedback input. connects fb1 to the center of a resistive voltage-divider between the boost regulator output and gnd to set the boost regulator output voltage. place the resistive voltage- divider within 5mm of fb1. 32 comp compensation pin for the step-up regulator error amplifier. connects a series resistor and capacitor from comp to ground. 33 thr vghm low-level regulation set-point input. connects thr to the center of a resistive voltage-divider between avdd and gnd to set the v ghm falling regulation level. the actual level is 10 x v thr . see the switch control section for details. 34 supp positive charge-pump drivers power supply. connects to the output of the boost regulator (avdd) and bypasses to cpgnd with a 0.1 f f capacitor. supp is internally connected to gd_i. 35 cpgnd charge pump and buck power ground 36 drvp positive charge-pump driver output. connects drvp to the positive charge-pump flying capacitor(s). 37 dly1 high-voltage switch array delay input. connects a capacitor from dly1 to gnd to set the delay time between when the positive charge pump finishes its soft-start and the startup of this high-voltage switch array. a 10 f a current source charges c dly1 . dly1 is internally pulled to gnd through 50 i resistance when en is low or when vl is below its uvlo threshold. 38 fbp positive charge-pump regulator feedback input. connects fbp to the center of a resistive voltage- divider between the positive charge-pump regulator output and gnd to set the positive charge-pump regulator output voltage. place the resistive voltage-divider within 5mm of fbp. 39 vgh switch input. source of the internal high-voltage p-channel mosfet between vgh and vghm. 40 vghm internal high-voltage mosfet switch common terminal. vghm is the output of the high-voltage switch-control block. 41 drn switch output. drain of the internal high-voltage p-channel mosfet connected to vghm. 42 supn negative charge-pump drivers power supply. bypass to cpgnd with a 0.1 f f capacitor. supn is inter- nally connected to in2. 43 drvn negative charge-pump driver output. connects drvn to the negative charge-pump flying capacitor(s). 45 fbn negative charge-pump regulator feedback input. connect fbn to the center of a resistive voltage- divider between the negative output and ref to set the negative charge-pump regulator output voltage. place the resistive voltage-divider within 5mm of fbn. 46 ref reference output. connects a 0.22 f f capacitor from ref to gnd. all power outputs are disabled until ref exceeds its uvlo threshold. 47 vref_fb gamma reference feedback input. connect vref_fb to the center of a resistive voltage-divider between vref_o and gnd to set the gamma reference output voltage. place the resistive voltage- divider within 5mm of vref_fb. 48 vref_o gamma reference output ep exposed pad. connects ep to gnd, and ties ep to a copper plane or island. maximizes the area of this copper plane or island to improve thermal performance. www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A 18 _____________________________________________________________________________________ figure 1. typical operating circuit c1 in2 in2 d1 vin 12v bst c2 lx1 lx1 l1 10h 0.1f d2 0.1uf c14 0.1f avdd c5 0.1f vin c4 0.1f supp vgh drvp 0.1f c11 1f c15 33pf out 3.3v, 1.5a invl out fb2 lx2 lx2 l2 1f vl vl gref vghm vcom avdd 16v, 1a r comp 25ki vgoff -6v, 50ma vgh 35v, 50ma vref_o 0.22f ref ref gnd avdd vref_i vref_fb supn drvn c10 0.1f d4 fbn fbp cpgnd r9 r10 from tcon gvoff thr drn ognd opo opn fsel on/off en dly1 unconnected or 150nf ss 1.61ki 1f 1.3nf r5 ref r6 r3 r4 d3 c12 c13 d5 13.3ki 2.2ki 10ki vghm comp 1ki pgnd pgnd 3 150f c comp 1nf 0.1f vin opp vop vdet pgood clim gd q1 fb1 r7 68.1ki r8 422ki gd_i 13.3ki 2.2ki r1 r2 c3 vl (or 3.3v) max17126 MAX17126A www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A ______________________________________________________________________________________ 19 typical operating circuit the typical operating circuit (figure 1) of the max17126/ MAX17126A comprise a complete power-supply system for tft lcd tv panels. the circuit generates a +3.3v logic supply, a +16v source driver supply, a +35v posi - tive gate-driver supply, a -6v negative gate-driver supply, and a p 0.5% high-accuracy, high-voltage gamma refer - ence. table 1 lists some selected components and table 2 lists the contact information for component suppliers. detailed description the max17126 /MAX17126A are multiple-output power supplies designed primarily for tft lcd tv panels. it contains a step-down switching regulator to generate the supply for system logic, a step-up switching regulator to generate the supply for source driver, and two charge- pump regulators to generate the supplies for tft gate drivers, a high-accuracy, high-voltage reference supply for gamma correction. each regulator features adjust - able output voltage, digital soft-start, and timer-delayed fault protection. both the step-down and step-up regula - tors use fixed-frequency current-mode control architec - ture. the two switching regulators are 180 n out of phase to minimize the input ripple. the internal oscillator offers two pin-selectable frequency options (500khz/750khz), allowing users to optimize their designs based on the specific application requirements. the step-up regu - lator also features adjustable current limit that can be adjusted through a resistor at the clim pin. the max17126/MAX17126A include one high-performance operational amplifier designed to drive the lcd back - plane (vcom). the amplifier features high-output cur - rent ( p 200ma), fast slew rate (45v/ f s), wide bandwidth (20mhz), and rail-to-rail outputs. the high-accuracy, high-voltage gamma reference has its error controlled to within p 0.5% and can deliver more than 60ma current. in addition, the max17126 /MAX17126A feature a high- voltage switch-control block, an internal 5v linear regula - tor, a 1.25v reference output, well-defined power-up and power-down sequences, and fault and thermal-overload protection. figure 2 shows the max17126 /MAX17126A functional diagram. table 1. component list table 2. operating mode designation description c1Cc4 10ff p q 10%, 25v x5r ceramic capacitors (1206) murata grm31cr61e106k tdk c3216x5r1e106m c5 22ff q 10%, 6.3v x5r ceramic capacitor (0805) murata grm21br60j226k tdk c2012x5r0j226k d1, d2 schottky diodes 30v, 3a (m-flat) toshiba cms02 d3, d4, d5 dual diodes 30v, 200ma (3 sot23) zetex bat54s fairchild bat54s l1 inductor, 10 f h, 3a, 45mi inductor (8.3mm x 9.5mm x 3mm) coiltronics sd8328-100-r sumida cdrh8d38np-100n (8.3mm x 8.3mm x 4mm) l2 inductor, 4.7 f h, 3a, 24.7mi inductor (8.3mm x 9.5mm x 3mm) coiltronics sd8328-4r7-r sumida cdrh8d38np-4r7n (8.3mm x 8.3mm x 4mm) supplier phone fax website fairchild semiconductor 408-822-2000 408-822-2102 www.fairchildsemi.com sumida corp. 847-545-6700 847-545-6720 www.sumida.com tdk corp. 847-803-6100 847-390-4405 www.component.tdk.com toshiba america electronic components, inc. 949-455-2000 949-859-3963 www.toshiba.com/taec www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A 20 _____________________________________________________________________________________ figure 2. functional diagram vin lx1 l1 pgnd avdd from tcon vcom vl (or 3.3v) fb1 comp step-up reg step-down reg osc positive charge pump negative charge pump gamma ref ref vl 150mv high- voltage switch block sequence clim gd_i gd pgood vdet vcom amp opp vop opn opo ognd drn thr fsel vghm vgh vin ref vghm vgh supp gd_i drvp on/off bst supn 50% osc cpgnd cpgnd fbp in2 fbn drvn vref_o vref_i ss vref_fb ref vgoff gvoff avdd dly1 gnd ref gref en avdd ref vl invl fb2 out lx2 in2 vl out vin vl www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A ______________________________________________________________________________________ 21 step-down regulator the step-down regulator consists of an internal n-chan - nel mosfet with gate driver, a lossless current-sense network, a current-limit comparator, and a pwm con - troller block. the external power stage consists of a schottky diode rectifier, an inductor, and output capaci - tors. the output voltage is regulated by changing the duty cycle of the high-side mosfet. a bootstrap circuit that uses a 0.1 f f flying capacitor between lx2 and bst provides the supply voltage for the high-side gate driver. although the max17126 /MAX17126A also include a 10i (typ) low-side mosfet, this switch is used to charge the bootstrap capacitor during startup and maintains fixed- frequency operation at light load and cannot be used as a synchronous rectifier. an external schottky diode (d2 in figure 1) is always required. pwm controller block the heart of the pwm control block is a multi-input, open- loop comparator that sums three signals: the output- voltage signal with respect to the reference voltage, the current-sense signal, and the slope-compensation signal. the pwm controller is a direct-summing type, lacking a traditional error amplifier and the phase shift associated with it. this direct-summing configuration approaches ideal cycle-by-cycle control over the output voltage. the step-down controller always operates in fixed-fre - quency pwm mode. each pulse from the oscillator sets the main pwm latch that turns on the high-side switch until the pwm comparator changes state. as the high- side switch turns off, the low-side switch turns on. the low-side switch stays on until the beginning of the next clock cycle. current limiting and lossless current sensing the current-limit circuit turns off the high-side mosfet switch whenever the voltage across the high-side mosfet exceeds an internal threshold. the actual cur - rent limit is typically 3.2a for max17126 and 3.5a for MAX17126A. for current-mode control, an internal lossless sense network derives a current-sense signal from the inductor dcr. the time constant of the current-sense network is not required to match the time constant of the inductor and has been chosen to provide sufficient current ramp signal for stable operation at both operating frequencies. the current-sense signal is ac-coupled into the pwm comparator, eliminating most dc output-voltage varia - tion with load current. dual-mode feedback the step-down regulator of the max17126 /MAX17126A support both fixed output and adjustable output. connect fb2 to gnd to enable the 3.3v fixed-output voltage. connect a resistive voltage-divider between out and gnd with the center tap connected to fb2 to adjust the output voltage. choose rb (resistance from fb2 to gnd) to be between 5k i and 50ki , and solve for ra (resis- tance from out to fb2) using the equation: out fb2 v ra rb - 1 v ? ? = ? ? ? ? where v fb2 = 1.25v, and v out may vary from 1.5v to 5v. because fb2 is a very sensitive pin, a noise filter is gen - erally required for fb2 in adjustable-mode operation. place an 82pf capacitor from fb2 to gnd to prevent unstable operation. no filter is required for 3.3v fixed- mode operation. soft-start the step-down regulator includes a 7-bit soft-start dac that steps its internal reference voltage from zero to 1.25v in 128 steps. the soft-start period is 3ms (typ) and fb2 fault detection is disabled during this period. the soft-start feature effectively limits the inrush current during startup (see the step-down regulator soft-start waveforms in the typical operating characteristics ). step-up regulator the step-up regulator employs a current-mode, fixed-fre - quency pwm architecture to maximize loop bandwidth and provide fast-transient response to pulsed loads typical of tft lcd panel source drivers. the integrated mosfet and the built-in digital soft-start function reduce the number of external components required while controlling inrush currents. the output voltage can be set from v in to 16.5v with an external resistive voltage- divider. the regulator controls the output voltage and the power delivered to the output by modulating duty cycle d of the internal power mosfet in each switching cycle. the duty cycle of the mosfet is approximated by: avdd diode in avdd diode lx1 v v - v d v v - v + + where v avdd is the output voltage of the step-up regu - lator, v diode is the voltage drop across the diode, and v lx1 is the voltage drop across the internal mosfet. www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A 22 _____________________________________________________________________________________ pwm controller block an error amplifier compares the signal at fb1 to 1.25v and changes the comp output. the voltage at comp sets the peak inductor current. as the load varies, the error amplifier sources or sinks current to the comp output accordingly to produce the inductor peak cur - rent necessary to service the load. to maintain stabil - ity at high duty cycles, a slope compensation signal is summed with the current-sense signal. on the rising edge of the internal clock, the controller sets a flip-flop, turning on the n-channel mosfet and applying the input voltage across the inductor. the current through the inductor ramps up linearly, storing energy in its magnetic field. once the sum of the current- feedback signal and the slope compensation exceed the comp voltage, the controller resets the flip-flop and turns off the mosfet. since the inductor current is continuous, a transverse potential develops across the inductor that turns on diode d1. the voltage across the inductor then becomes the difference between the out - put voltage and the input voltage. this discharge condi - tion forces the current through the inductor to ramp back down, transferring the energy stored in the magnetic field to the output capacitor and the load. the mosfet remains off for the rest of the clock cycle. step-up regulator external pmos pass switch as shown in figure 1, a series external p-channel mosfet can be installed between the cathode of the step-up regulator schottky catch diode and the v avdd filter capacitors. this feature is used to sequence power to avdd after the max17126 /MAX17126A have pro - ceeded through normal startup to limit input surge current during the output capacitor initial charge, and to provide true shutdown when the step-up regulator is disabled. when en is low, gd is internally pulled up to the gd_i through a 25 i resistor. once en is high and the negative charge-pump regulator is in regulation, the gd starts pull - ing down with a 10 f a (typ) internal current source. the external p-channel mosfet turns on and connects the cathode of the step-up regulator schottky catch diode to the step-up regulator load capacitors when gd falls below the turn-on threshold of the mosfet. when v gd reaches v gd_i - 6v(gd done), the step-up regulator is enabled and initiates a soft-start routine. when not using this feature, leave gd high impedance, and connect gd_i to the output of the step-up converter. soft-start the step-up regulator achieves soft-start by linearly ramping up its internal current limit. the soft-start is either done internally when the capacitance on pin ss is < 200pf or externally when capacitance on pin ss is > 200pf. the internal soft-start ramps up the current limit in 128 steps in 12ms. the external soft-start terminates when the ss pin voltage reaches 1.25v. the soft-start feature effectively limits the inrush current during startup (see the step-up regulator soft-start waveforms in the typical operating characteristics ). positive charge-pump regulator the positive charge-pump regulator (figure 3) is typically used to generate the positive supply rail for the tft lcd gate driver ics. the output voltage is set with an external resistive voltage-divider from its output to gnd with the midpoint connected to fbp. the number of charge-pump stages and the setting of the feedback divider determine figure 3. positive charge-pump regulator block diagram max17126 MAX17126A d3 c14 c15 vgh ref 1.25v gd_i error amplifier osc positive charge-pump regulator c13 c12 d5 p1 n1 drvp fbp cpgnd supp www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A ______________________________________________________________________________________ 23 the output voltage of the positive charge-pump regula - tor. the charge pump includes a high-side p-channel mosfet (p1) and a low-side n-channel mosfet (n1) to control the power transfer as shown in figure 3. during the first half cycle, n1 turns on and charges flying capacitors c12 and c13 (figure 3). during the second half cycle, n1 turns off and p1 turns on, level shifting c12 and c13 by v supp volts. if the voltage across c15 (v gh ) plus a diode drop (vd) is smaller than the level-shifted flying-capacitor voltage (vc13) plus v supp , charge flows from c13 to c15 until the diode (d3) turns off. the amount of charge transferred to the output is determined by the error amplifier that controls n1s on-resistance. each time it is enabled, the positive charge-pump regu - lator goes through a soft-start routine by ramping up its internal reference voltage from 0 to 1.25v in 128 steps. the soft-start period is 2ms (typ) and fbp fault detec - tion is disabled during this period. the soft-start feature effectively limits the inrush current during startup. negative charge-pump regulator the negative charge-pump regulator is typically used to generate the negative supply rail for the tft lcd gate driver ics. the output voltage is set with an external resistive voltage-divider from its output to ref with the midpoint connected to fbn. the number of charge-pump stages and the setting of the feedback divider determine the output of the negative charge-pump regulator. the charge-pump controller includes a high-side p-channel mosfet (p2) and a low-side n-channel mosfet (n2) to control the power transfer as shown in figure 4. during the first half cycle, p2 turns on, and flying capacitor c10 charges to v supn minus a diode drop (figure 4). during the second half cycle, p2 turns off, and n2 turns on, level shifting c10. this connects c10 in parallel with reservoir capacitor c11. if the voltage across c11 minus a diode drop is greater than the voltage across c10, charge flows from c11 to c10 until the diode (d4) turns off. the amount of charge transferred from the output is determined by the error amplifier that controls n2s on- resistance. figure 4. negative charge-pump regulator block diagram max17126 MAX17126A d4 ref c11 vgoff ref 0.25v r5 in2 error amplifier osc r6 negative charge-pump regulator c10 p2 n2 drvn fbn cpgnd supn www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A 24 _____________________________________________________________________________________ the negative charge-pump regulator is enabled after the step-down regulator finishes soft-start. each time it is enabled, the negative charge-pump regulator goes through a soft-start routine by ramping down its internal reference voltage from 1.25v to 250mv in 128 steps. the soft-start period is 1.8ms (typ) and fbn fault detection is disabled during this period. the soft-start feature effectively limits the inrush current during startup. high-voltage switch control the max17126 /MAX17126As high-voltage switch control block (figure 5) consists of two high-voltage p-channel mosfets: q1, between vgh, and vghm and q2, between vghm and drn. the switch control block is enabled when v dly1 exceeds v ref . q1 and q2 are controlled by gvoff. when gvoff is logic-high, q1 turns on and q2 turns off, connecting vghm to vgh. when gvoff is logic- low, q1 turns off and q2 turns on, connecting vghm to drn. vghm can then be discharged through a resistor connected between drn and gnd or avdd. q2 turns off and stops discharging vghm when vghm reaches 10 times the voltage on thr. the switch control block is disabled and dly1 is held low when the lcd is shut down or in a fault state. operational amplifier the operational amplifier is typically used to drive the lcd backplane (vcom). it features q 200ma output short-circuit current, 45v/ f s slew rate, and 20mhz/3db bandwidth. the rail-to-rail input and output capability maximizes system flexibility. short-circuit current limit and input clamp the operational amplifier limits short-circuit current to approximately q 200ma if the output is directly shorted to vop or to ognd. if the short-circuit condition persists, the junction temperature of the ic rises until it reaches the thermal-shutdown threshold (+160 n c typ). once the junction temperature reaches the thermal-shutdown threshold, an internal thermal sensor immediately sets the thermal fault latch, shutting off all the ics outputs. the device remains inactive until the input voltage is cycled. the operational amplifiers have 4v input clamp structures in series with a 500 i resistance and a diode (figure 6). figure 5. switch control max17126 MAX17126A 9r v ref r 1ki q4 q2 q1 gd done en shdn fault ref 10a dly1 gvoff vghm thr vgh drn www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A ______________________________________________________________________________________ 25 driving pure capacitive load the lcd backplane consists of a distributed series capacitance and resistance, a load that can be easily driven by the operational amplifier. however, if the operational amplifier is used in an application with a pure capacitive load, steps must be taken to ensure stable operation. as the operational amplifiers capacitive load increases, the amplifiers bandwidth decreases and gain peaking increases. a 5 i to 50i small resistor placed between opo and the capacitive load reduces peaking, but also reduces the gain. an alternative method of reducing peaking is to place a series rc network (snubber) in parallel with the capacitive load. the rc network does not continuously load the output or reduce the gain. typical values of the resistor are between 100 i and 200 i , and the typical value of the capacitor is 10nf. linear regulator (vl) the max17126 /MAX17126A include an internal linear regulator. invl is the input of the linear regulator. the input voltage range is between 8v and 16.5v. the output voltage is set to 5v. the regulator powers the internal mosfet drivers, pwm controllers, charge-pump regulators, and logic circuitry. the total external load capability is 25ma. bypass vl to gnd with a minimum 1ff ceramic capacitor. reference voltage (ref) the reference output is nominally 1.25v, and can source at least 50 f a (see typical operating characteristics ). vl is the input of the internal reference block. bypass ref with a 0.22 f f ceramic capacitor connected between ref and gnd. high-accuracy, high-voltage gamma reference the ldo is typically used to drive gamma-correction divider string. its output voltage is adjustable through a resistor-divider. this ldo features high output accuracy (q 0.5%) and low-dropout voltage (0.25v typ) and can supply at least 60ma. pgood function pgood is an open-drain output that connects to gnd when vdet is below its detection threshold (1.25v typ). pgood is active after vl rises above uvlo threshold. frequency selection and out-of-phase operation (fsel) the step-down regulator and step-up regulator use the same internal oscillator. the fsel input selects the switching frequency. table 3 shows the switching frequency based on the fsel connection. high-frequency (750khz) operation optimizes the application for the smallest component size, trading off efficiency due to higher switching losses. low-frequency (500khz) operation offers the best overall efficiency at the expense of component size and board space. to reduce the input rms current, the step-down regulator and the step-up regulator operate 180 n out of phase from each other. the feature allows the use of less input capacitance. figure 6. op amp input clamp structure table 3. frequency selection max17126 MAX17126A 4v 500 opn opp opo vop ognd fsel switching frequency (khz) vl, invl, or float 750 gnd 500 www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A 26 _____________________________________________________________________________________ power-up sequence the step-down regulator starts up when the max17126 / MAX17126A s internal reference voltage (ref) is above its undervoltage lockout (uvlo) threshold. once the step-down regulator soft-start is done, the fb2 fault- detection circuit and the negative charge pump are enabled. negative charge-pump fault protection is enabled after its own soft-start is done. when en goes to logic-high, a 10a current source starts to pull down on gd, turning on the external gd_i- avdd pmos switch. when v gd reaches gd-done threshold (v gd_i - 6v), the step-up regulator is enabled. gamma reference is enabled at the same time. the max17126/MAX17126A simplify system design by including an internal 12ms soft-start for the step-up regulator. when the capacitor on the ss pin is less than 200pf, the internal 12ms soft-start is in place. this saves one capacitor from system design. if an external capaci - tor greater than 200pf is used, a 5a current source charges the ss capacitor pin and when the ss voltage reaches 1.25v, soft-start is done. the fb1 fault-detection circuit is enabled after this soft-start is done. the positive charge pump is also enabled after the step-up regulator finishes its soft-start. after the positive charge pumps soft-start is done, the fbp fault-detection circuit is enabled, as well as the high-voltage switch delay block. c dly1 is charged with an internal 10a current source and v dly1 rises linearly. when v dly1 reaches ref, the high-voltage switch block is enabled. figure 7. power-up sequence boost fault blank negative charge-pump fault blank positive charge -pump fault blank buck fault blank dly1 time time positive charge-pump regulator output negative charge-pump regulator output vl ref in/invl buck output en invl uvlo avdd gd done gd ref time vghm unconnected vghm depends on gvoff ref ss vghm time ref uvlo vl uvlo gref time pgood t ss t ss t ss t ss www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A ______________________________________________________________________________________ 27 power-down sequence the step-down regulator, step-up regulator, positive charge pump, negative charge pump, and high-voltage switching block all start to shut down when invl drops below its uvlo threshold. vl stays flat until invl does not have enough headroom. reference ref starts to fall after vl drops below its uvlo threshold. gamma reference gref stays flat until avdd does not have enough headroom. a pmos switch turns on after vl drops below its uvlo threshold to guarantee gref does not go over avdd. pgood is pulled low after its input voltage (buck output in this case) drops below the designed threshold. after vl drops below its uvlo threshold, pgood gives up control and is resistively pulled up to its input voltage. the high-voltage switching block output vghm falls until vl drops below its uvlo threshold, after which it is in high impedance. fault protection during steady-state operation, if any output of the four regulators output (step-down regulator, step-up regulator, positive charge-pump regulator, and negative charge-pump regulator) goes lower than its respective fault-detection threshold, the max17126 activates an internal fault timer. if any condition or the combination of conditions indicates a continuous fault for the fault timer duration (50ms typ), the MAX17126A latches off all its outputs while the max17126 latches off all the outputs except the buck regulator (latched off only when the fault happens on its output). if a short has happened to any of the four regulator outputs, no fault timer is applied; the part latches off immediately. pay special attention to shorts on the step- up regulator and positive charge pump. make sure when a short happens, negative ringing on vref_i (connected to step-up regulator output) and vgh (connected to positive charge-pump output) does not exceed absolute maximum ratings . otherwise, physical damage of the part may occur. cycle the input voltage to clear the fault latch and restart the supplies. thermal-overload protection the thermal-overload protection prevents excessive power dissipation from overheating the max17126 / MAX17126A . when the junction temperature exceeds t j = +160 n c, a thermal sensor immediately activates the fault protection that shuts down all the outputs. cycle the input voltage to clear the fault latch and restart the max17126/MAX17126A. the thermal-overload protection protects the controller in the event of fault conditions. for continuous operation, do not exceed the absolute maximum junction temperature rating of t j = +150nc. design procedure step-down regulator inductor selection three key inductor parameters must be specified: inductance value (l), peak current (i peak ), and dc resistance (r dc ). the following equation includes a constant, lir, which is the ratio of peak-to-peak inductor ripple current to dc load current. a higher lir value allows smaller inductance, but results in higher losses and higher ripple. a good compromise between size and losses is typically found at a 30% ripple current-to- load current ratio (lir = 0.3) that corresponds to a peak inductor current 1.15 times the dc load current: ( ) out in2 out 2 in2 sw out(max) v v - v l v f i lir = figure 8. power-down sequence time time ref invl negative charge-pump regulator output positive charge-pump regulator output buck invl uvlo avdd time vghm unconnected vghm depends on gvoff vghm time vl uvlo gref time pgood vl output www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A 28 _____________________________________________________________________________________ where i out(max) is the maximum dc load current, and the switching frequency f sw is 750khz when fsel is tied to vl, 500khz when fsel is tied to gnd. the exact inductor value is not critical and can be adjusted to make trade-offs among size, cost, and efficiency. lower inductor values minimize size and cost, but they also increase the output ripple and reduce the efficiency due to higher peak currents. on the other hand, higher inductor values increase efficiency, but at some point resistive losses due to extra turns of wire exceed the benefit gained from lower ac current levels. the inductors saturation current must exceed the peak inductor current. the peak current can be calculated by: ( ) out in2 out out_ripple sw 2 in2 v v - v i f l v = out_ripple out_peak out(max) i i i 2 = + the inductors dc resistance should be low for good efficiency. find a low-loss inductor having the lowest possible dc resistance that fits in the allotted dimensions. ferrite cores are often the best choice. shielded- core geometries help keep noise, emi, and switching waveform jitter low. considering the typical operation circuit in figure 1, the maximum load current i out(max) is 1.5a with a 3.3v output and a typical 12v input voltage. choosing an lir of 0.4 at this operation point: 2 3.3v (12v - 3.3v) l 5.3 h 12v 750khz 1.5a 0.4 = f pick l 2 = 4.7 f h. at that operation point, the ripple current and the peak current are: ( ) out_ripple 3.3v 12v - 3.3v i 0.68a 750khz 4.7 h 12v = = f out_peak 0.68a i 1.5a 1.84a 2 = + = input capacitors the input filter capacitors reduce peak currents drawn from the power source and reduce noise and voltage ripple on the input caused by the regulators switching. they are usually selected according to input ripple current requirements and voltage rating, rather than capacitance value. the input voltage and load current determine the rms input ripple current (i rms ): ( ) out in2 out rms out in2 v v - v i i v = the worst case is i rms = 0.5 x i out that occurs at v in2 = 2 x v out . for most applications, ceramic capacitors are used because of their high ripple current and surge current capabilities. for optimal circuit long-term reliability, choose an input capacitor that exhibits less than +10 nc temperature rise at the rms input current corresponding to the maximum load current. output capacitor selection since the max17126 /MAX17126A s step-down regulator is internally compensated, it is stable with any reasonable amount of output capacitance. however, the actual capacitance and equivalent series resistance (esr) affect the regulators output ripple voltage and transient response. the rest of this section deals with how to determine the output capacitance and esr needs according to the ripple voltage and load-transient requirements. the output voltage ripple has two components: variations in the charge stored in the output capacitor, and the voltage drop across the capacitors esr caused by the current into and out of the capacitor: out_ripple out_ripple(esr) out_ripple(c) v v v = + out_ripple(esr) out_ripple esr_out v i r = out_ripple out_ripple(c) out sw i v 8 c f = where i out _ ripple is defined in the step-down regulator inductor selection section, c out (c5 in figure 1) is the output capacitance, and r esr _ out is the esr of the output capacitor c out . in figure 1s circuit, the inductor ripple current is 0.68a. if the voltage-ripple requirement of figure 1s circuit is p 1% of the 3.3v output, then the total peak-to-peak ripple voltage should be less than 66mv. assuming that the esr ripple and the capacitive ripple each should be less than 50% of the total peak-to-peak ripple, then the esr should be less than 48.5m i and the output capacitance should be more than 3.4 f f to meet the total ripple requirement. a 22 f f capacitor with esr (including pcb trace resistance) of 10m i is selected for the typical operating circuit in figure 1, which easily meets the voltage ripple requirement. www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A ______________________________________________________________________________________ 29 the step-down regulators output capacitor and esr also affect the voltage undershoot and overshoot when the load steps up and down abruptly. the undershoot and overshoot also have two components: the voltage steps caused by esr, and voltage sag and soar due to the finite capacitance and inductor slew rate. use the following formulas to check if the esr is low enough and the output capacitance is large enough to prevent excessive soar and sag. the amplitude of the esr step is a function of the load step and the esr of the output capacitor: out_esr_step out esr_out v i r = d the amplitude of the capacitive sag is a function of the load step, the output capacitor value, the inductor value, the input-to-output voltage differential, and the maximum duty cycle: ( ) 2 2 out out_sag out in2(min) max out l ( i ) v 2 c v d - v = d the amplitude of the capacitive soar is a function of the load step, the output capacitor value, the inductor value, and the output voltage: 2 2 out out_soar out out l ( i ) v 2 c v = d keeping the full-load overshoot and undershoot less than 3% ensures that the step-down regulators natural integrator response dominates. given the component values in the circuit of figure 1, during a full 1.5a step load transient, the voltage step due to capacitor esr is negligible. the voltage sag and soar are 76mv and 73mv, respectively. rectifier diode the max17126 /MAX17126A s high switching frequency demands a high-speed rectifier. schottky diodes are recommended for most applications because of their fast recovery time and low forward voltage. in general, a 2a schottky diode works well in the max17126 /MAX17126A s step-up regulator. step-up regulator inductor selection the inductance value, peak current rating, and series resistance are factors to consider when selecting the inductor. these factors influence the converters efficiency, maximum output load capability, transient response time, and output voltage ripple. physical size and cost are also important factors to be considered. the maximum output current, input voltage, output voltage, and switching frequency determine the inductor value. very high inductance values minimize the current ripple, and therefore, reduce the peak current, which decreases core losses in the inductor and i 2 r losses in the entire power path. however, large inductor values also require more energy storage and more turns of wire that increase physical size and can increase i 2 r losses in the inductor. low inductance values decrease the physical size, but increase the current ripple and peak current. finding the best inductor involves choosing the best compromise between circuit efficiency, inductor size, and cost. the equations used here include a constant lir, which is the ratio of the inductor peak-to-peak ripple current to the average dc inductor current at the full-load current. the best trade-off between inductor size and circuit efficiency for step-up regulators generally has an lir between 0.3 and 0.5. however, depending on the ac characteristics of the inductor core material and ratio of inductor resistance to other power-path resistances, the best lir can shift up or down. if the inductor resistance is relatively high, more ripple can be accepted to reduce the number of turns required and increase the wire diameter. if the inductor resistance is relatively low, increasing inductance to lower the peak current can decrease losses throughout the power path. if extremely thin high-resistance inductors are used, as is common for lcd panel applications, the best lir can increase to between 0.5 and 1.0. once a physical inductor is chosen, higher and lower values of the inductor should be evaluated for efficiency improvements in typical operating regions. calculate the approximate inductor value using the typical input voltage (v in ), the maximum output current (i avdd(max) ), the expected efficiency ( e typ ) taken from an appropriate curve in the typical operating characteristics , and an estimate of lir based on the above discussion: 2 in avdd in typ 1 avdd avdd(max) sw v v - v l v i f lir ? ? ? ? ? ? = ? ? ? ? ? ? ? ? ? ? ? ? ? ? choose an available inductor value from an appropriate inductor family. calculate the maximum dc input current at the minimum input voltage v in(min) using conservation of energy and the expected efficiency at that operating point ( e min ) taken from an appropriate curve in the typical operating characteristics: avdd(max) avdd in(dc,max) in(min) min i v i v = www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A 30 _____________________________________________________________________________________ calculate the ripple current at that operating point and the peak current required for the inductor: ( ) in(min) avdd in(min) avdd_ripple avdd avdd sw v v - v i l v f = avdd_ripple avdd_peak in(dc,max) i i i 2 = + the inductors saturation current rating and the max17126/ MAX17126As lx1 current limit should exceed i avdd _ peak and the inductors dc current rating should exceed i in(dc,max) . for good efficiency, choose an inductor with less than 0.1 i series resistance. considering the typical operating circuit (figure 1), the maximum load current (i avdd(max) ) is 1a with a 16v output and a typical input voltage of 12v. choosing an lir of 0.3 and estimating efficiency of 90% at this operating point: 2 1 12v 16v - 12v 90% l 9 h 16v 1a 750khz 0.3 ? ? ? ?? ? = = ? ? ? ?? ? ? ? ? ?? ? f using the circuits minimum input voltage (8v) and estimating efficiency of 85% at that operating point: in(dc,max) 1a 16v i 2.35a 8v 85% = the ripple current and the peak current are: ( ) avdd_ripple 8v 16v - 8v i 0.53a 10 h 16v 750khz = f avdd_peak 0.53a i 2.35a 2.62a 2 = + output capacitor selection the total output voltage ripple has two components: the capacitive ripple caused by the charging and discharging of the output capacitance, and the ohmic ripple due to the capacitors equivalent series resistance (esr): avdd_ripple avdd_ripple(c) avdd_ripple(esr ) v v v = + avdd avdd in avdd_ripple(c) avdd avdd sw i v - v v c v f ? ? ? ? ? ? and: avdd_ripple(esr) avdd_peak esr_avdd v i r where i avdd _ peak is the peak inductor current (see the inductor selection section). for ceramic capacitors, the output voltage ripple is typically dominated by v avdd _ ripple(c) . the voltage rating and temperature characteristics of the output capacitor must also be considered. note that all ceramic capacitors typically have large temperature coefficient and bias voltage coefficients. the actual capacitor value in circuit is typically significantly less than the stated value. input capacitor selection the input capacitor reduces the current peaks drawn from the input supply and reduces noise injection into the ic. a 22 f f ceramic capacitor is used in the typical operating circuit (figure 1) because of the high source impedance seen in typical lab setups. actual applications usually have much lower source impedance since the step-up regulator often runs directly from the output of another regulated supply. typically, the input capacitance can be reduced below the values used in the typical operating circuit. rectifier diode the max17126/MAX17126As high switching frequency demands a high-speed rectifier. schottky diodes are recommended for most applications because of their fast recovery time and low forward voltage. in general, a 2a schottky diode complements the internal mosfet well. output voltage selection the output voltage of the step-up regulator can be adjusted by connecting a resistive voltage-divider from the output (v avdd ) to gnd with the center tap connected to fb1 (see figure 1). select r2 in the 10k i to 50ki range. calculate r1 with the following equation: avdd fb1 v r1 r2 - 1 v ? ? = ? ? ? ? where v fb1 , the step-up regulators feedback set point, is 1.25v. place r1 and r2 close to the ic. loop compensation choose r comp to set the high-frequency integrator gain for fast-transient response. choose c comp to set the integrator zero to maintain loop stability. for low-esr output capacitors, use the following equations to obtain stable performance and good transient response: in avdd avdd comp avdd avdd(max) 100 v v c r l i avdd avdd comp avdd(max) comp v c c 10 i r www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A ______________________________________________________________________________________ 31 to further optimize transient response, vary r comp in 20% steps and c comp in 50% steps while observing transient response waveforms. charge-pump regulators selecting the number of charge-pump stages for highest efficiency, always choose the lowest number of charge-pump stages that meet the output requirement. the number of positive charge-pump stages is given by: gh dropout avdd pos supp d v v - v n v - 2 v + = where n pos is the number of positive charge-pump stages, v gh is the output of the positive charge-pump regulator, v supp is the supply voltage of the charge- pump regulators, v d is the forward voltage drop of the charge-pump diode, and v dropout is the dropout margin for the regulator. use v dropout = 300mv. the number of negative charge-pump stages is given by: goff dropout neg supn d -v v n v - 2 v + = where n neg is the number of negative charge-pump stages and v goff is the output of the negative charge- pump regulator. the above equations are derived based on the assumption that the first stage of the positive charge pump is connected to v avdd and the first stage of the negative charge pump is connected to ground. sometimes fractional stages are more desirable for better efficiency. this can be done by connecting the first stage to v out or another available supply. if the first charge-pump stage is powered from v out , then the above equations become: gh dropout out pos supp d v v - v n v - 2 v + = goff dropout out neg supn d -v v v n v - 2 v + + = flying capacitors increasing the flying capacitor cx (connected to drvp and drvn) value lowers the effective source impedance and increases the output current capability. increasing the capacitance indefinitely has a negligible effect on output current capability because the internal switch resistance and the diode impedance place a lower limit on the source impedance. a 0.1 f f ceramic capacitor works well in most low-current applications. the flying capacitors voltage rating must exceed the following: cx pos(neg) supp(supn) v n v > where n pos(neg) is the number of stages in which the flying capacitor appears. it is the same as the number of charge-pump stages. charge-pump output capacitor increasing the output capacitance or decreasing the esr reduces the output ripple voltage and the peak-to-peak transient voltage. with ceramic capacitors, the output voltage ripple is dominated by the capacitance value. use the following equation to approximate the required capacitor value: load_cp out_cp sw ripple_cp i c 2 f v r where c out _ cp is the output capacitor of the charge pump, i load _ cp is the load current of the charge pump, and v ripple_cp is the peak-to-peak value of the output ripple. output voltage selection adjust the positive charge-pump regulators output voltage by connecting a resistive voltage-divider from vgh output to gnd with the center tap connected to fbp (figure 1). select the lower resistor of divider r4 in the 10ki to 30ki range. calculate upper resistor r3 with the following equation: vgh fbp v r3 r4 - 1 v ? ? = ? ? ? ? where v fbp = 1.25v (typ). adjust the negative charge-pump regulators output voltage by connecting a resistive voltage-divider from v goff to ref with the center tap connected to fbn (figure 1). select r6 in the 20k i to 68ki range. calculate r5 with the following equation: fbn goff ref fbn v - v r5 r6 v - v = where v fbn = 250mv, v ref = 1.25v. note that ref can only source up to 50 f a, using a resistor less than 20ki , for r6 results in a higher bias current than ref can supply. www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A 32 _____________________________________________________________________________________ high-accuracy, high-voltage gamma reference output-voltage selection the output voltage of the high-accuracy ldo is set by connecting a resistive voltage-divider from the output (v ref_o ) to agnd with the center tap connected to v ref_fb (see figure 1). select r10 in the 10k i to 50ki range. calculate r9 with the following equation: ref_o ref_fb v r9 r10 -1 v ? ? = ? ? ? ? ? ? where v ref_fb , the ldos feedback set point, is 1.25v. place r9 and r10 close to the ic. input and output capacitor selection to ensure stability of the ldo, use a minimum of 1 ff on the regulators input (v ref_i ) and a minimum of 2.2ff on the regulators output (v ref_o ). place the capacitors near the pins and connect their ground connections directly together. set the pgood threshold voltage pgood threshold voltage can be adjusted by connecting a resistive voltage-divider from input v in to gnd with the center tap connected to v det (see figure 1). select r8 in the 10k i to 50ki range. calculate r7 with the following equation: ? ? = ? ? ? ? in_pgood det v r7 r8 -1 v where v det = 1.25v is the v det threshold set point. v in_pgood is the desired pgood threshold voltage. place r7 and r8 close to the ic. pcb layout and grounding careful pcb layout is important for proper operation. use the following guidelines for good pcb layout: u minimize the area of respective high-current loops by placing each dc/dc converters inductor, diode, and output capacitors near its input capacitors and its lx_ and pgnd pins. for the step-down regulator, the high-current input loop goes from the positive terminal of the input capacitor to the ics in2 pin, out of lx2, to the inductor, to the positive terminals of the output capacitors, reconnecting the output capaci - tor and input capacitor ground terminals. the high- current output loop is from the inductor to the positive terminals of the output capacitors, to the negative terminals of the output capacitors, and to the schottky diode (d2). for the step-up regulator, the high-current input loop goes from the positive terminal of the input capacitor to the inductor, to the ics lx1 pin, out of pgnd, and to the input capacitors negative terminal. the high-current output loop is from the positive ter - minal of the input capacitor to the inductor, to the out - put diode (d1), to the positive terminal of the output capacitors, reconnecting between the output capaci - tor and input capacitor ground terminals. connect these loop components with short, wide connections. avoid using vias in the high-current paths. if vias are unavoidable, use many vias in parallel to reduce resistance and inductance. u create a power ground island for the step-down regulator, consisting of the input and output capaci - tor grounds and the diode ground. connect all these together with short, wide traces or a small ground plane. similarly, create a power ground island (pgnd) for the step-up regulator, consisting of the input and output capacitor grounds and the pgnd pin. create a power ground island (cpgnd) for the positive and negative charge pumps, consisting of supp and output (v gh , v goff ) capacitor grounds, and negative charge-pump diode ground. connect the step-down regulator ground plane, pgnd ground plane, and cpgnd ground plane together with wide traces. maximizing the width of the power ground traces improves efficiency and reduces output volt - age ripple and noise spikes. u create an analog ground plane (gnd) consisting of the gnd pin, all the feedback divider ground con - nections, the comp, ss, and dly1 capacitor ground connections, and the devices exposed backside pad. connect the pgnd and gnd islands by con - necting the two ground pins directly to the exposed backside pad. make no other connections between these separate ground planes. u place all feedback voltage-divider resistors as close as possible to their respective feedback pins. the dividers center trace should be kept short. placing the resistors far away causes their fb traces to become antennas that can pick up switching noise. care should be taken to avoid running any feedback trace near lx1, lx2, drvp, or drvn. u place in2 pin, vl pin, ref pin, and v ref_o pin bypass capacitors as close as possible to the device. the ground connection of the vl bypass capacitor should be connected directly to the gnd pin with a wide trace. www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A ______________________________________________________________________________________ 33 u minimize the length and maximize the width of the traces between the output capacitors and the load for best transient responses. u minimize the size of the lx1 and lx2 nodes while keeping them wide and short. keep the lx1 and lx2 nodes away from feedback nodes (fb1, fb2, fbp, fbn, and vref_fb) and analog ground. use dc traces as shield if necessary. refer to the max17126 evaluation kit for an example of proper board layout. pin configuration chip information process: bicmos package information for the latest package outline information and land patterns, go to www.maxim-ic.com/packages. package type package code outline no. land pattern no. 48 tqfn t4877-3 21-0144 90-0129 top view max17126 MAX17126A thin qfn 13 14 15 16 17 18 19 20 21 22 23 24 lx2 lx2 bst in2 in2 gnd vdet invl vl fsel clim ss 48 47 46 45 44 43 42 41 40 39 38 37 1 2 3 4 5 6 7 8 9 10 11 12 vref_o vref_fb ref fbn gnd drvn supn drn vghm vgh fbp dly1 n.c. out fb2 en gvoff pgood opo opn opp ognd vop vref_i 36 35 34 33 32 31 30 29 28 27 26 25 lx1 lx1 pgnd pgnd gd_i gd fb1 comp thr supp cpgnd drvp www.datasheet.co.kr datasheet pdf - http://www..net/
multi-output power supplies with vcom amplifier and high-voltage gamma reference for lcd tvs max17126/MAX17126A maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circuit patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. 34 maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ? 2010 maxim integrated products maxim is a registered trademark of maxim integrated products, inc. revision history revision number revision date description pages changed 0 6/09 initial release 1 3/10 MAX17126A added to data sheet 1 -33 www.datasheet.co.kr datasheet pdf - http://www..net/

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