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| general description the max1908/max8724/max8765/MAX8765A highly integrated, multichemistry battery-charger control ics simplify the construction of accurate and efficient charg- ers. these devices use analog inputs to control charge current and voltage, and can be programmed by the host or hardwired. the max1908/max8724/max8765/ MAX8765A achieve high efficiency using a buck topology with synchronous rectification. the max1908/max8724/max8765/MAX8765A feature input current limiting. this feature reduces battery charge current when the input current limit is reached to avoid overloading the ac adapter when supplying the load and the battery charger simultaneously. the max1908/max8724/max8765/MAX8765A provide out- puts to monitor current drawn from the ac adapter (dc input source), battery-charging current, and the pres- ence of an ac adapter. the max1908? conditioning charge feature provides 300ma to safely charge deeply discharged lithium-ion (li+) battery packs. the max1908 includes a conditioning charge feature while the max8724/max8765 /MAX8765A do not. the max1908/max8724/max8765/MAX8765A charge two to four series li+ cells, providing more than 5a, and are available in a space-saving, 28-pin, thin qfn package (5mm 5mm). an evaluation kit is available to speed designs. applications notebook and subnotebook computers personal digital assistants handheld terminals features 0.5% output voltage accuracy using internal reference (0.4% for MAX8765A, 2-/3-cell only) 4% accurate input current limiting 5% accurate charge current analog inputs control charge current and charge voltage outputs for monitoring current drawn from ac adapter charging current ac adapter presence up to 17.6v battery-voltage set point maximum 28v input voltage > 95% efficiency shutdown control input charge any battery chemistry li+, nicd, nimh, lead acid, etc. max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers ________________________________________________________________ maxim integrated products 1 28 + 27 26 25 24 23 22 iinp cssp cssn dhi bst lx dlov 8 9 10 11 12 13 14 shdn ichg acin acok refin ictl gnd 15 16 17 18 19 20 21 vctl batt cells csin csip pgnd dlo 7 6 5 4 3 2 1 ccv cci ccs ref cls ldo dcin max1908 max8724 max8765 MAX8765A thin qfn top view pin configuration ordering information max1908 max8724 max8765 MAX8765A ac adapter input to external load ldo from host p 10 h 0.015 ? batt+ dcin refin vctl ictl acin acok shdn ichg iinp ccv cci ccs cells ldo bst dlov dhi lx dlo pgnd csip csin batt ref cls gnd cssp cssn 0.01 ? minimum operating circuit 19-2764; rev 5; 11/09 for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. evaluation kit available part temp range pin-package max1908 eti+ -40? to +85? 28 thin qfn-ep* max8724 eti+ -40? to +85? 28 thin qfn-ep* max8765 eti+ -40? to +85? 28 thin qfn-ep* MAX8765A eti + -40? to +85? 28 thin qfn-ep* + denotes a lead(pb)-free/rohs-compliant package. * ep = exposed pad.
max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v dcin = v cssp = v cssn = 18v, v batt = v csip = v csin = 12v, v refin = 3v, v vctl = v ictl = 0.75 x v refin , cells = open, cls = ref, v bst - v lx = 4.5v, acin = gnd = pgnd = 0, c ldo = 1?, ldo = dlov, c ref = 1?; cci, ccs, and ccv are compensated per figure 1a; t a = 0c to +85c , unless otherwise noted. typical values are at t a = +25?.) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. dcin, cssp, cssn, acok to gnd.......................-0.3v to +30v bst to gnd ............................................................-0.3v to +36v bst to lx..................................................................-0.3v to +6v dhi to lx ...................................................-0.3v to (v bst + 0.3v) lx to gnd .................................................................-6v to +30v batt, csip, csin to gnd .....................................-0.3v to +20v csip to csin or cssp to cssn or pgnd to gnd ....................................................-0.3v to +0.3v cci, ccs, ccv, dlo, ichg, iinp, acin, ref to gnd.......................-0.3v to (v ldo + 0.3v) dlov, vctl, ictl, refin, cells, cls, ldo, shdn to gnd .............................................-0.3v to +6v dlov to ldo.........................................................-0.3v to +0.3v dlo to pgnd .........................................-0.3v to (v dlov + 0.3v) ldo short-circuit current...................................................50ma continuous power dissipation (t a = +70?) 28-pin thin qfn (5mm 5mm) (derate 20.8mw/? above +70?) .........................1666.7mw operating temperature range ..........................-40? to +85? junction temperature ......................................................+150? storage temperature range .............................-60? to +150? lead temperature (soldering, 10s) .................................+300? parameter symbol conditions min typ max units charge-voltage regulation v vctl = v refin -0.5 +0.5 v vctl = v refin /20 -0.5 +0.5 battery-regulation voltage accuracy (max1908/max8724/max8765 (2, 3, or 4 cells) and MAX8765A (4 cells only)) v vctl = v ldo -0.5 +0.5 % v vctl = v refin -0.4 +0.4 v vctl = v refin /20 -0.4 +0.4 battery-regulation voltage accuracy (MAX8765A, 2 or 3 cells only) v vctl = v ldo -0.4 +0.4 % vctl default threshold v vctl rising 4.0 4.1 4.2 v refin range (note 1) 2.5 3.6 v refin undervoltage lockout v refin falling 1.20 1.92 v charge-current regulation csip-to-csin full-scale current- sense voltage v ictl = v refin 71.25 75 78.75 mv v ictl = v refin -5 +5 v ictl = v refin x 0.6 -5 +5 v ictl = v ldo -6 +6 max8765/MAX8765A only; v ictl = v refin x 0.036 -45 +45 charging-current accuracy max8724 only; v ictl = v refin x 0.058 -33 +33 % charge-current gain error (max8765/MAX8765A only) -2 +2 % charge-current offset (max8765/MAX8765A only) -2 +2 mv ictl default threshold v ictl rising 4.0 4.1 4.2 v batt/csip/csin input voltage range 0 19 v max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers _______________________________________________________________________________________ 3 electrical characteristics (continued) (v dcin = v cssp = v cssn = 18v, v batt = v csip = v csin = 12v, v refin = 3v, v vctl = v ictl = 0.75 x v refin , cells = open, cls = ref, v bst - v lx = 4.5v, acin = gnd = pgnd = 0, c ldo = 1?, ldo = dlov, c ref = 1?; cci, ccs, and ccv are compensated per figure 1a; t a = 0c to +85c , unless otherwise noted. typical values are at t a = +25?.) parameter symbol conditions min typ max units v dcin = 0v or v ictl = 0v or v shdn = 0v 1 csip/csin input current charging 400 650 ? cycle-by-cycle maximum current limit rs2 = 0.015m ? 6.0 6.8 7.5 a ictl power-down mode threshold voltage (max1908/max8724 only) v vctl rising refin/ 100 refin/ 55 refin/ 33 v v vctl = v ictl = 0 or 3v -1 +1 ictl, vctl input bias current v dcin = 0v, v vctl = v ictl = v refin = 5v -1 +1 ? v dcin = 5v, v refin = 3v -1 +1 refin input bias current v refin = 5v -1 +1 ? ichg transconductance (max1908/max8724 only) g ichg v csip - v csin = 45mv 2.7 3 3.3 ?/mv ichg transconductance (max8765/MAX8765A only) g ichg v csip - v csin = 45mv 2.85 3 3.15 ?/mv ichg transconductance error (max8765/MAX8765A only) -5 +5 % ichg transconductance offset (max8765/MAX8765A only) -5 +5 ? v csip - v csin = 75mv -6 +6 v csip - v csin = 45mv -5 +5 ichg accuracy v csip - v csin = 5mv -40 +40 % ichg output current v csip - v csin = 150mv, v ichg = 0v 350 ? ichg output voltage v csip - v csin = 150mv, ichg = open 3.5 v input-current regulation cssp-to-cssn full-scale current-sense voltage 72 75 78 mv v cls = v ref -4 +4 v cls = v ref /2 -7.5 +7.5 input current-limit accuracy v cls = 1.1v (max8765/MAX8765A only) -10 +10 % input current-limit gain error (max8765/MAX8765A only) -2 +2 % input current-limit offset (max8765/MAX8765A only) -2 +2 mv cssp, cssn input voltage range 8 28 v v dcin = 0v 0.1 1 cssp, cssn input current (max1908/max8724 only) v cssp = v cssn = v dcin > 8v 350 600 ? v dcin = 0v 0.1 1 cssp input current (max8765/MAX8765A only) v cssp = v cssn = 28v v dcin = 28v 400 650 ? max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers 4 _______________________________________________________________________________________ electrical characteristics (continued) (v dcin = v cssp = v cssn = 18v, v batt = v csip = v csin = 12v, v refin = 3v, v vctl = v ictl = 0.75 x v refin , cells = open, cls = ref, v bst - v lx = 4.5v, acin = gnd = pgnd = 0, c ldo = 1?, ldo = dlov, c ref = 1?; cci, ccs, and ccv are compensated per figure 1a; t a = 0c to +85c , unless otherwise noted. typical values are at t a = +25?.) parameter symbol conditions min typ max units v dcin = 0v 0.1 1 cssn input current (max8765/MAX8765A only) v cssp = v cssn = 28v v dcin = 28v 0.1 1 ? cls input range (max1908/max8724 only) 1.6 ref v cls input range (max8765/MAX8765A only) 1.1 ref v cls input bias current v cls = 2v -1 +1 ? iinp transconductance (max1908/max8724 only) g iinp v cssp - v cssn = 75mv 2.7 3 3.3 ?/mv v cssp - v cssn = 75mv -5 +5 iinp accuracy v cssp - v cssn = 37.5mv -7.5 +7.5 % iinp transconductance (max8765/MAX8765A only) g iinp v cssp - v ccsn = 75mv 2.82 3 3.18 ?/mv iinp transconductance error (max8765/MAX8765A only) -6 +6 % iinp transconductance offset (max8765/MAX8765A only) -10 +10 ? iinp output current v cssp - v cssn = 150mv, v iinp = 0v 350 ? iinp output voltage v cssp - v cssn = 150mv, v iinp = open 3.5 v supply and ldo regulator dcin input voltage range v dcin 8 28 v v dcin falling 7 7.4 dcin undervoltage-lockout trip point v dcin rising 7.5 7.85 v dcin quiescent current i dcin 8.0v < v dcin < 28v 3.2 6 ma v batt = 19v, v dcin = 0v 1 batt input current i batt v batt = 2v to 19v, v dcin = 19.3v 200 500 ? ldo output voltage 8v < v dcin < 28v, no load 5.25 5.4 5.55 v ldo load regulation 0 < i ldo < 10ma 34 100 mv ldo undervoltage-lockout trip point v dcin = 8v 3.20 4 5.15 v reference ref output voltage 0 < i ref < 500? 4.072 4.096 4.120 v ref undervoltage-lockout trip point v ref falling 3.1 3.9 v max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers _______________________________________________________________________________________ 5 electrical characteristics (continued) (v dcin = v cssp = v cssn = 18v, v batt = v csip = v csin = 12v, v refin = 3v, v vctl = v ictl = 0.75 x v refin , cells = open, cls = ref, v bst - v lx = 4.5v, acin = gnd = pgnd = 0, c ldo = 1?, ldo = dlov, c ref = 1?; cci, ccs, and ccv are compensated per figure 1a; t a = 0c to +85c , unless otherwise noted. typical values are at t a = +25?.) parameter symbol conditions min typ max units trip points v dcin falling, referred to v csin (max1908/max8724 only) 50 100 150 batt power-fail threshold v cssp falling, referred to v csin (max8765/MAX8765A only) 50 100 150 mv batt power-fail threshold hysteresis 200 mv acin rising (max8765/MAX8765A only) 2.028 2.048 2.068 acin threshold acin rising (max1908/max8724 only) 2.007 2.048 2.089 v acin threshold hysteresis 0.5% of ref 20 mv acin input bias current v acin = 2.048v -1 +1 ? switching regulator dhi off-time v batt = 16v, v dcin = 19v, v cells = v refin 0.36 0.4 0.44 ? dhi minimum off-time v batt = 16v, v dcin = 17v, v cells = v refin 0.24 0.28 0.33 ? dhi maximum on-time 2.5 5 7.5 ms dlov supply current dlo low 5 10 ? bst supply current dhi high 6 15 ? bst input quiescent current v dcin = 0v, v bst = 24.5v, v batt = v lx = 20v 0.3 1 ? lx input bias current v dcin = 28v, v batt = v lx = 20v 150 500 ? lx input quiescent current v dcin = 0v, v batt = v lx = 20v 0.3 1 ? dhi maximum duty cycle 99 99.9 % minimum discontinuous-mode ripple current 0.5 a battery undervoltage charge current v batt = 3v per cell (rs2 = 15m ? ), max1908 only, v batt rising 150 300 450 ma cells = gnd, max1908 only, v batt rising 6.1 6.2 6.3 cells = open, max1908 only, v batt rising 9.15 9.3 9.45 battery undervoltage current threshold cells = v refin , max1908 only, v batt rising 12.2 12.4 12.6 v dhi on-resistance high v bst - v lx = 4.5v, i dhi = +100ma 4 7 ? dhi on-resistance low v bst - v lx = 4.5v, i dhi = -100ma 1 3.5 ? dlo on-resistance high v dlov = 4.5v, i dlo = +100ma 4 7 ? dlo on-resistance low v dlov = 4.5v, i dlo = -100ma 1 3.5 ? max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers 6 _______________________________________________________________________________________ electrical characteristics (continued) (v dcin = v cssp = v cssn = 18v, v batt = v csip = v csin = 12v, v refin = 3v, v vctl = v ictl = 0.75 x v refin , cells = open, cls = ref, v bst - v lx = 4.5v, acin = gnd = pgnd = 0, c ldo = 1?, ldo = dlov, c ref = 1?; cci, ccs, and ccv are compensated per figure 1a; t a = 0c to +85c , unless otherwise noted. typical values are at t a = +25?.) parameter symbol conditions min typ max units error amplifiers gmv amplifier transconductance gmv v v c t l = v ld o , v bat t = 16.8v , c e lls = v re f in 0.0625 0.125 0.2500 ?/mv gmi amplifier transconductance gmi v ictl = v re f in , v csip - v csin = 75mv 0.5 1 2.0 ?/mv gms amplifier transconductance gms v cls = v ref , v cssp - v cssn = 75mv 0.5 1 2.0 ?/mv cci, ccs, ccv clamp voltage 0.25v < v ccv,ccs,cci < 2v 150 300 600 mv logic levels cells input low voltage 0.4 v cells input open voltage cells = open (v refin /2) - 0.2v v r e f in / 2 ( v r e f in /2) + 0.2v v cells input high voltage v refin - 0.4v v cells input bias current cells = 0v or v re f in -2 +2 ? acok and shdn acok input voltage range 0 28 v acok sink current v a cok = 0.4v, v acin = 3v 1 ma acok leakage current v a cok = 28v, v acin = 0v 1 ? shdn input voltage range 0 ldo v v shdn = 0v or v ldo -1 +1 shdn input bias current v shdn = 0v or v shdn = 5v -1 +1 ? shdn threshold v s hdn falling 22 23.5 25 % of v refin shdn threshold hysteresis 1 % of v refin max1908/max8724/max8765/MAX8765A electrical characteristics (v dcin = v cssp = v cssn = 18v, v batt = v csip = v csin = 12v, v refin = 3v, v vctl = v ictl = 0.75 x v refin , cells = open, cls = ref, v bst - v lx = 4.5v, acin = gnd = pgnd = 0, c ldo = 1?, ldo = dlov, c ref = 1?; cci, ccs, and ccv are compensated per figure 1a; t a = -40c to +85c , unless otherwise noted.) (note 2) parameter symbol conditions min typ max units charge-voltage regulation v vctl = v refin -0.6 +0.6 v vctl = v refin /20 -0.6 +0.6 battery regulation voltage accuracy (2, 3, or 4 cells) v vctl = v ldo -0.6 +0.6 % refin range (note 1) 2.5 3.6 v refin undervoltage lockout v refin falling 1.92 v charge current regulation csip-to-csin full-scale current- sense voltage v ictl = v refin 70.5 79.5 mv v ictl = v refin -6 +6 v ictl = v refin x 0.6 -7.5 +7.5 v ictl = v ldo -7.5 +7.5 max8765/MAX8765A only; v ictl = v refin x 0.036 -50 +50 charging-current accuracy max8724 only; v ictl = v refin x 0.058 -33 +33 % charge-current gain error (max8765/MAX8765A only) -2 +2 % charge-current offset (max8765/MAX8765A only) -2 +2 mv batt/csip/csin input voltage range 0 19 v v dcin = 0v or v ictl = 0v or v shdn = 0v 1 csip/csin input current charging 650 ? cycle-by-cycle maximum current limit i max rs2 = 0.015 ? 6.0 7.5 a ictl power-down mode threshold voltage (max1908/max8724 only) v ictl rising refin/ 100 refin/ 33 v ichg transconductance (max1908/max8724 only) g ichg v csip - v csin = 45mv 2.7 3.3 ?/mv ichg transconductance (max8765/MAX8765A only) g ichg v csip - v csin = 45mv 2.785 3.225 ?/mv ichg transconductance error (max8765/MAX8765A only) -7.5 +7.5 % ichg transconductance offset (max8765/MAX8765A only) -6.5 +6.5 ? low-cost multichemistry battery chargers _______________________________________________________________________________________ 7 max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers 8 _______________________________________________________________________________________ electrical characteristics (continued) (v dcin = v cssp = v cssn = 18v, v batt = v csip = v csin = 12v, v refin = 3v, v vctl = v ictl = 0.75 x v refin , cells = open, cls = ref, v bst - v lx = 4.5v, acin = gnd = pgnd = 0, c ldo = 1?, ldo = dlov, c ref = 1?; cci, ccs, and ccv are compensated per figure 1a; t a = -40c to +85c , unless otherwise noted.) (note 2) parameter symbol conditions min typ max units v csip - v csin = 75mv -7.5 +7.5 v csip - v csin = 45mv -7.5 +7.5 ichg accuracy v csip - v csin = 5mv -40 +40 % input-current regulation cssp-to-cssn full-scale current-sense voltage 71.25 78.75 mv v cls = v ref -5 +5 v cls = v ref /2 -7.5 +7.5 input current-limit accuracy v cls = 1.1v (max8765/MAX8765A only) -10 +10 % input current-limit gain error (max8765/MAX8765A only) -2 +2 % input current-limit offset (max8765/MAX8765A only) -2 +2 mv cssp, cssn input voltage range 8 28 v v dcin = 0v 1 cssp, cssn input current (max1908/max8724 only) v cssp = v cssn = v dcin > 8v 600 ? v dcin = 0v 1 cssp input current (max8765/MAX8765A only) v cssp = v cssn = 28v v dcin = 28v 650 ? v dcin = 0v 1 cssn input current (max8765/MAX8765A only) v cssp = v cssn = 28v v dcin = 28v 1 ? cls input range (max1908/max8724 only) 1.6 ref v cls input range (max8765/MAX8765A only) 1.1 ref v iinp transconductance (max1908/max8724 only) g iinp v cssp - v cssn = 75mv 2.7 3.3 ?/mv iinp transconductance (max8765/MAX8765A only) g iinp v cssp - v ccsn = 75mv 2.785 3.225 ?/mv iinp transconductance error (max8765/MAX8765A only) -7.5 +7.5 % iinp transconductance offset (max8765/MAX8765A only) -12 +12 ? v cssp - v cssn = 75mv -7.5 +7.5 iinp accuracy v cssp - v cssn = 37.5mv -7.5 +7.5 % max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers _______________________________________________________________________________________ 9 electrical characteristics (continued) (v dcin = v cssp = v cssn = 18v, v batt = v csip = v csin = 12v, v refin = 3v, v vctl = v ictl = 0.75 x v refin , cells = open, cls = ref, v bst - v lx = 4.5v, acin = gnd = pgnd = 0, c ldo = 1?, ldo = dlov, c ref = 1?; cci, ccs, and ccv are compensated per figure 1a; t a = -40c to +85c , unless otherwise noted.) (note 2) parameter symbol conditions min typ max units supply and ldo regulator dcin input voltage range v dcin 8 28 v dcin quiescent current i dcin 8.0v < v dcin < 28v 6 ma v batt = 19v, v dcin = 0v 1 batt input current i batt v batt = 2v to 19v, v dcin = 19.3v 500 ? ldo output voltage 8v < v dcin < 28v, no load 5.25 5.55 v ldo load regulation 0 < i ldo < 10ma 100 mv reference ref output voltage 0 < i ref < 500? 4.065 4.120 v trip points v dcin falling, referred to v csin (max1908/max8724 only) 50 150 batt power-fail threshold v cssp falling, referred to v csin (max8765/MAX8765A only) 50 150 mv acin rising ( max8765/MAX8765A only) 2.028 2.068 acin threshold acin rising (max1908/max8724 only) 2.007 2.089 v switching regulator dhi off-time v batt = 16v, v dcin = 19v, v cells = v refin 0.35 0.45 ? dhi minimum off-time v batt = 16v, v dcin = 17v, v cells = v refin 0.24 0.33 ? dhi maximum on-time 2.5 7.5 ms dhi maximum duty cycle 99 % battery undervoltage charge current v batt = 3v per cell (rs2 = 15m ? ), max1908 only, v batt rising 150 450 ma cells = gnd, max1908 only, v batt rising 6.09 6.30 cells = open, max1908 only, v batt rising 9.12 9.45 battery undervoltage current threshold cells = v refin , max1908 only, v batt rising 12.18 12.60 v dhi on-resistance high v bst - v lx = 4.5v, i dhi = +100ma 7 ? dhi on-resistance low v bst - v lx = 4.5v, i dhi = -100ma 3.5 ? dlo on-resistance high v dlov = 4.5v, i dlo = +100ma 7 ? dlo on-resistance low v dlov = 4.5v, i dlo = -100ma 3.5 ? max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers 10 ______________________________________________________________________________________ electrical characteristics (continued) (v dcin = v cssp = v cssn = 18v, v batt = v csip = v csin = 12v, v refin = 3v, v vctl = v ictl = 0.75 x v refin , cells = open, cls = ref, v bst - v lx = 4.5v, acin = gnd = pgnd = 0, c ldo = 1?, ldo = dlov, c ref = 1?; cci, ccs, and ccv are compensated per figure 1a; t a = -40c to +85c , unless otherwise noted.) (note 2) parameter symbol conditions min typ max units error amplifiers gmv amplifier transconductance gmv v v c t l = v ld o , v bat t = 16.8v , c e lls = v re f in 0.0625 0.250 ?/mv gmi amplifier transconductance gmi v ictl = v re f in , v csip - v csin = 75mv 0.5 2.0 ?/mv gms amplifier transconductance gms v cls = v ref , v cssp - v cssn = 75mv 0.5 2.0 ?/mv cci, ccs, ccv clamp voltage 0.25v < v ccv,ccs,cci < 2v 150 600 mv logic levels cells input low voltage 0.4 v cells input open voltage cells = open (v refin /2) - 0.2v ( v r e f in /2) + 0.2v v cells input high voltage v refin - 0.4v v acok and shdn acok input voltage range 0 28 v acok sink current v acok = 0.4v, v acin = 3v 1 ma shdn input voltage range 0 ldo v shdn threshold v shdn falling 22 25 % of v refin note 1: if both ictl and vctl use default mode (connected to ldo), refin is not used and can be connected to ldo. note 2: specifications to t a = -40? are guaranteed by design and not production tested. load-transient response (battery insertion and removal) max1908 toc01 1ms/div i batt 2a/div v batt 5v/div v cci 500mv/div v ccv 500mv/div ictl = ldo vctl = ldo ccv cci load-transient response (step in-load current) max1908 toc02 1ms/div v batt 2v/div v cci 500mv/div v ccs 500mv/div 16.8v 0 0 load current 5a/div adapter current 5a/div ictl = ldo charging current = 3a v batt = 16.8v load step = 0 to 4a i source limit = 5a ccs ccs cci cci v batt 2v/div 0 0 0 charge current 2a/div load current 5a/div adapter current 5a/div load-transient response (step in-load current) max1908 toc03 1ms/div ictl = ldo charging current = 3a v batt = 16.8v load step = 0 to 4a i source limit = 5a typical operating characteristics (circuit of figure 1, v dcin = 20v, t a = +25?, unless otherwise noted.) max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers ______________________________________________________________________________________ 11 inductor current 500ma/div v dcin 10v/div v batt 500mv/div line-transient response max1908 toc04 10ms/div ictl = ldo vctl = ldo i charge = 3a line step 18.5v to 27.5v -1.0 -0.8 -0.9 -0.6 -0.7 -0.4 -0.5 -0.3 -0.1 -0.2 0 0 234 1 567 9 810 ldo load regulation max1908 toc05 ldo current (ma) v ldo error (%) v ldo = 5.4v -0.05 -0.03 -0.04 -0.01 -0.02 0.01 0 0.02 0.04 0.03 0.05 8 121416 10 18 20 22 26 24 28 ldo line regulation max1908 toc06 v in (v) v ldo error (%) i ldo = 0 v ldo = 5.4v -0.10 -0.07 -0.08 -0.09 -0.06 -0.05 -0.04 -0.03 -0.02 -0.01 0 0 200 100 300 400 500 ref voltage load regulation max1908 toc07 ref current ( a) v ref error (%) -0.10 -0.04 -0.06 -0.08 -0.02 0 0.02 0.04 0.06 0.08 0.10 -40 10 -15 35 60 85 ref voltage error vs. temperature max1908 toc08 temperature ( c) v ref error (%) 90 0 0.01 10 1 0.1 efficiency vs. charge current 30 10 70 50 100 40 20 80 60 max1908 toc09 charge current (a) efficiency (%) v batt = 16v v batt = 8v v batt = 12v 0 100 50 250 200 150 300 350 450 400 500 046 2 8 10 12 14 16 18 20 22 frequency vs. v in - v batt max1908 toc10 (v in - v batt ) (v) frequency (khz) i charge = 3a vctl = ictl = ldo 3 cells 4 cells -0.4 -0.1 -0.3 -0.5 0 0.2 0.3 0.4 0.5 01234 output v/i characteristics max1908 toc11 batt current (a) batt voltage error (%) 0.1 -0.2 2 cells 3 cells 4 cells 0 0.02 0.01 0.03 0.06 0.07 0.05 0.04 0.08 0 0.2 0.3 0.4 0.5 0.1 0.6 0.7 0.8 0.9 1.0 batt voltage error vs. vctl max1908 toc12 vctl/refin (%) batt voltage error (%) 4 cells refin = 3.3v no load typical operating characteristics (continued) (circuit of figure 1, v dcin = 20v, t a = +25?, unless otherwise noted.) max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers 12 ______________________________________________________________________________________ -1 1 0 3 2 4 5 01.0 0.5 1.5 2.0 current-setting error vs. ictl max1908 toc13 v ictl (v) current-setting error (%) v refin = 3.3v 0 1.5 1.0 0.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 01.0 0.5 1.5 2.0 2.5 3.0 ichg error vs. charge current max1908 toc14 i batt (a) ichg (%) v batt = 16v v batt = 12v v batt = 8v v refin = 3.3v -40 -30 -20 -10 0 10 20 30 40 01234 iinp error vs. system load current max1908 toc15 system load current (a) iinp error (%) i batt = 0 -80 -60 -40 -20 0 20 40 60 80 0 0.5 1.0 1.5 2.0 iinp error vs. input current max1908 toc16 input current (a) iinp error (%) system load = 0 error due to switching noise typical operating characteristics (continued) (circuit of figure 1, v dcin = 20v, t a = +25?, unless otherwise noted.) max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers ______________________________________________________________________________________ 13 pin description pin name function 1 dcin charging voltage input. bypass dcin with a 1? capacitor to pgnd. 2 ldo d evi ce p ow er s up p l y. outp ut of the 5.4v l i near r eg ul ator sup p l i ed fr om d c in . byp ass w i th a 1 f cap aci tor to gn d . 3 cls source current-limit input. voltage input for setting the current limit of the input source. 4 ref 4.096v voltage reference. bypass ref with a 1? capacitor to gnd. 5 ccs input-current regulation loop-compensation point. connect a 0.01? capacitor to gnd. 6 cci output-current regulation loop-compensation point. connect a 0.01? capacitor to gnd. 7 ccv voltage regulation loop-compensation point. connect 1k ? in series with a 0.1? capacitor to gnd. 8 shdn shutdown control input. drive shdn logic low to shut down the max1908/max8724/max8765 MAX8765A. use with a thermistor to detect a hot battery and suspend charging. 9 ichg charge-current monitor output. ichg is a scaled-down replica of the charger output current. use ichg to monitor the charging current and detect when the chip changes from constant-current mode to constant- voltage mode. the transconductance of (csip - csin) to ichg is 3?/mv. 10 acin ac detect input. input to an uncommitted comparator. acin can be used to detect ac-adapter presence. 11 acok ac detect output. high-voltage open-drain output is high impedance when v acin is less than v ref /2. 12 refin reference input. allows the ictl and vctl inputs to have ratiometric ranges for increased accuracy. 13 ictl output current-limit set input. ictl input voltage range is v refin /32 to v refin . the max1908/max8724 shut down if ictl is forced below v refin /100 while the max8765/MAX8765A does not. when ictl is equal to ldo, the set point for csip - csin is 45mv. 14 gnd analog ground 15 vctl output voltage-limit set input. vctl input voltage range is 0 to v refin . when vctl is equal to ldo, the set point is (4.2 x cells)v. 16 batt battery voltage input 17 cells cell count input. tri-level input for setting number of cells. gnd = 2 cells, open = 3 cells, refin = 4 cells. 18 csin output current-sense negative input 19 csip output current-sense positive input. connect a current-sense resistor from csip to csin. 20 pgnd power ground 21 dlo low-side power mosfet driver output. connect to low-side nmos gate. 22 dlov low-side driver supply. bypass dlov with a 1? capacitor to gnd. 23 lx high-side power mosfet driver power-return connection. connect to the source of the high-side nmos. 24 bst high-side power mosfet driver power-supply connection. connect a 0.1? capacitor from lx to bst. 25 dhi high-side power mosfet driver output. connect to high-side nmos gate. 26 cssn input current-sense negative input 27 cssp input current-sense positive input. connect a current-sense resistor from cssp to cssn. 28 iinp input-current monitor output. iinp is a scaled-down replica of the input current. iinp monitors the total system current. the transconductance of (cssp - cssn) to iinp is 3?/mv. max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers 14 ______________________________________________________________________________________ detailed description the max1908/max8724/max8765/MAX8765A include all the functions necessary to charge li+ batteries. a high-efficiency synchronous-rectified step-down dc-dc converter controls charging voltage and current. the device also includes input-source current limiting and analog inputs for setting the charge current and charge voltage. control charge current and voltage using the ictl and vctl inputs, respectively. both ictl and vctl are ratiometric with respect to refin, allowing compatibility with dacs or microcontrollers (?s). ratiometric ictl and vctl improve the accuracy of the charge current and voltage set point by matching v re- fin to the reference of the host. for standard applica- tions, internal set points for ictl and vctl provide 3a charge current (with 0.015 ? sense resistor), and 4.2v (per cell) charge voltage. connect ictl and vctl to ldo to select the internal set points. the max1908 safely conditions overdischarged cells with 300ma (with 0.015 ? sense resistor) until the battery-pack voltage exceeds 3.1v number of series-connected cells. the shdn input allows shutdown from a microcontroller or thermistor. the dc-dc converter uses external n-channel mosfets as the buck switch and synchronous rectifier to convert the input voltage to the required charging current and voltage. the typical application circuit shown in figure 1 uses a ? to control charging cur- rent, while figure 2 shows a typical application with charging voltage and current fixed to specific values for the application. the voltage at ictl and the value of rs2 set the charging current. the dc-dc converter generates the control signals for the external mosfets to regulate the voltage and the current set by the vctl, ictl, and cells inputs. the max1908/max8724/max8765/MAX8765A feature a voltage regulation loop (ccv) and two current regula- tion loops (cci and ccs). the ccv voltage regulation loop monitors batt to ensure that its voltage does not exceed the voltage set by vctl. the cci battery cur- rent regulation loop monitors current delivered to batt to ensure that it does not exceed the current limit set by ictl. a third loop (ccs) takes control and reduces the battery-charging current when the sum of the system load and the battery-charging input current exceeds the input current limit set by cls. setting the battery-regulation voltage the max1908/max8724/max8765/MAX8765A use a high-accuracy voltage regulator for charging voltage. the vctl input adjusts the charger output voltage. vctl control voltage can vary from 0 to v refin , provid- ing a 10% adjustment range on the v batt regulation voltage. by limiting the adjust range to 10% of the regu- lation voltage, the external resistor mismatch error is reduced from 1% to 0.05% of the regulation voltage. therefore, an overall voltage accuracy of better than 0.7% is maintained while using 1% resistors. the per- cell battery termination voltage is a function of the bat- tery chemistry. consult the battery manufacturer to determine this voltage. connect vctl to ldo to select the internal default setting v batt = 4.2v number of cells, or program the battery voltage with the following equation: cells is the programming input for selecting cell count. connect cells as shown in table 2 to charge 2, 3, or 4 li+ cells. when charging other cell chemistries, use cells to select an output voltage range for the charger. the internal error amplifier (gmv) maintains voltage regulation (figure 3). the voltage error amplifier is compensated at ccv. the component values shown in figures 1 and 2 provide suitable performance for most applications. individual compensation of the voltage reg- ulation and current regulation loops allows for optimal compensation (see the compensation section). v cells v v v batt vctl refin =+ ? ? ? ? ? ? ? ? ? ? ? ? 404 . table 2. cell-count programming description max1908 max8724 max8765/ MAX8765A conditioning charge feature yes no no ictl shutdown mode yes yes no acok enable condition refin must be ready refin must be ready independent of refin table 1. versions comparison cells cell count gnd 2 open 3 v refin 4 max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers ______________________________________________________________________________________ 15 max1908/max8724/max8765/MAX8765A dcin ldo max1908 max8724 max8765 MAX8765A cls ref gnd cells dlov ac adapter input 8.5v to 28v 12.6v output voltage 7.5a input current limit dhi d3 bst smart battery host acin d2 r6 59k ? 1% r7 19.6k ? 1% c5 1 f vctl ictl refin acok ichg iinp r8 1m ? r9 20k ? r10 10k ? c14 0.1 f c20 0.1 f ccv c11 0.1 f r5 1k ? cci ccs c10 0.01 f c9 0.01 f c12 1 f c1 2 10 f c13 1 f c15 0.1 f lx c16 1 f ldo r13 33 ? cssp cssn open (3 cells select) d1 rs1 0.01 ? l1 10 h rs2 0.015 ? csip csin pgnd dlo n1b n1a batt c4 22 f batt + r19, r20, r21 10k ? avdd/ref scl sda temp batt- adc input adc input output dac output v cc scl sda adc input gnd pgnd gnd to external load shdn 0.1 f 0.1 f figure 1. ?-controlled typical application circuit typical application circuits max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers 16 ______________________________________________________________________________________ to external load max1908 max8724 max8765 MAX8765A cls ref gnd cells refin (4 cells select) dlov ac adapter input 8.5v to 28v dhi d3 bst battery acin d2 ldo ldo 16.8v output voltage 2.5a charge limit 4a input current limit r6 59k ? 1% r7 19.6k ? 1% r11 15k ? r12 12k ? c5 1 f c12 1.5nf shdn ichg iinp r19 10k ? 1% r20 10k ? 1% ccv c11 0.1 f r5 1k ? cci ccs c10 0.01 f c9 0.01 f c12 1 f c1 2 10 f c13 1 f c15 0.1 f lx c16 1 f ldo r13 33 ? cssp cssn rs1 0.01 ? l1 10 h rs2 0.015 ? csip csin pgnd dlo n1b n1a from host p (shutdown) n batt gnd pgnd c4 22 f batt + refin vctl dcin batt- thm ictl r14 10.5k ? 1% r15 8.25k ? 1% r16 8.25k ? 1% p1 r17 19.1k ? 1% r18 22k ? 1% acok 0.01 f 0.01 f figure 2. typical application circuit with fixed charging parameters typical application circuits (continued) max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers ______________________________________________________________________________________ 17 max1908/max8724/max8765/MAX8765A max1908 max8724 max8765 MAX8765A logic block gms shdn gnd cls ccs cssp cssn csip csin ictl cci batt cells ccv vctl 23.5% refin gnd dcin srdy 5.4v linear regulator 1/55 ictl max1908/max8724 only ref/2 rdy 4v cell select logic 4.096v reference lvc refin csi bat_uv 3.1v/cell r1 lvc dcin ldo ref refin acin acok iinp ichg bst dhi lx dlov dlo pgnd max1908 only x 75mv ref level shifter x 75mv refin x 400mv refin dc-dc converter gmi gmv gm level shifter n gm level shifter driver driver figure 3. functional diagram functional diagram max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers 18 ______________________________________________________________________________________ setting the charging-current limit the ictl input sets the maximum charging current. the current is set by current-sense resistor rs2, connected between csip and csin. the full-scale differential voltage between csip and csin is 75mv; thus, for a 0.015 ? sense resistor, the maximum charging current is 5a. battery-charging current is programmed with ictl using the equation: the input voltage range for ictl is v refin /32 to v refin . the max1908/max8724 shut down if ictl is forced below v refin /100 (min), while the max8765/MAX8765A does not. connect ictl to ldo to select the internal default full- scale, charge-current sense voltage of 45mv. the charge current when ictl = ldo is: where rs2 is 0.015 ? , providing a charge-current set point of 3a. the current at the ichg output is a scaled-down replica of the battery output current being sensed across csip and csin (see the current measurement section). when choosing the current-sense resistor, note that the voltage drop across this resistor causes further power loss, reducing efficiency. however, adjusting ictl to reduce the voltage across the current-sense resistor can degrade accuracy due to the smaller signal to the input of the current-sense amplifier. the charging- current-error amplifier (gmi) is compensated at cci (see the compensation section). setting the input current limit the total input current (from an ac adapter or other dc source) is a function of the system supply current and the battery-charging current. the input current regulator limits the input current by reducing the charging current when the input current exceeds the input current-limit set point. system current normally fluc- tuates as portions of the system are powered up or down. without input current regulation, the source must be able to supply the maximum system current and the maximum charger input current simultaneously. by using the input current limiter, the current capability of the ac adapter can be lowered, reducing system cost. the max1908/max8724/max8765/MAX8765A limit the battery charge current when the input current-limit threshold is exceeded, ensuring the battery charger does not load down the ac adapter voltage. an internal amplifier compares the voltage between cssp and cssn to the voltage at cls. v cls can be set by a resistive divider between ref and gnd. connect cls to ref for the full-scale input current limit. the cls volt- age range for the max1908/max8724 is from 1.6v to ref, while the max8765/m ax8765a cls voltage is from 1.1v to ref. the input current is the sum of the device current, the charger input current, and the load current. the device current is minimal (3.8ma) in comparison to the charge and load currents. determine the actual input current required as follows: where is the efficiency of the dc-dc converter. v cls determines the reference voltage of the gms error amplifier. sense resistor rs1 and v cls determine the maximum allowable input current. calculate the input current limit as follows: once the input current limit is reached, the charging current is reduced until the input current is at the desired threshold. when choosing the current-sense resistor, note that the voltage drop across this resistor causes further power loss, reducing efficiency. choose the smallest value for rs1 that achieves the accuracy requirement for the input current-limit set point. conditioning charge the max1908 includes a battery-voltage comparator that allows a conditioning charge of overdischarged li+ battery packs. if the battery-pack voltage is less than 3.1v number of cells programmed by cells, the max1908 charges the battery with 300ma current when using sense resistor rs2 = 0.015 ? . after the battery voltage exceeds the conditioning charge thresh- old, the max1908 resumes full-charge mode, charging to the programmed voltage and current limits. the max8724/max8765/MAX8765A do not offer this feature. ac adapter detection connect the ac adapter voltage through a resistive divider to acin to detect when ac power is available, as shown in figure 1. acin voltage rising trip point is v ref /2 with 20mv hysteresis. acok is an open-drain output and is high impedance when acin is less than i v vrs input cls ref = 0 075 1 . ii iv v input load chg batt in =+ ? ? ? ? ? ? i v rs chg = 0 045 2 . i v vrs chg ictl refin = 0 075 2 . max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers ______________________________________________________________________________________ 19 v ref /2. since acok can withstand 30v (max), acok can drive a p-channel mosfet directly at the charger input, providing a lower dropout voltage than a schottky diode (figure 2). in the max1908/max8724 the acok comparator is enabled after refin is ready. in the max8765 /MAX8765A, the acok comparator is independent of refin. current measurement use ichg to monitor the battery-charging current being sensed across csip and csin. the ichg voltage is proportional to the output current by the equation: v ichg = ichg x rs2 x g ichg x r9 where i chg is the battery-charging current, g ichg is the transconductance of ichg (3?/mv typ), and r9 is the resistor connected between ichg and ground. leave ichg unconnected if not used. use iinp to monitor the system input current being sensed across cssp and cssn. the voltage of iinp is proportional to the input current by the equation: v iinp = i input x rs1 x g iinp x r10 where i input is the dc current being supplied by the ac adapter power, g iinp is the transconductance of iinp (3?/mv typ), and r10 is the resistor connected between iinp and ground. ichg and iinp have a 0 to 3.5v output voltage range. leave iinp unconnected if not used. ldo regulator ldo provides a 5.4v supply derived from dcin and can deliver up to 10ma of load current. the mosfet drivers are powered by dlov and bst, which must be connected to ldo as shown in figure 1. ldo supplies the 4.096v reference (ref) and most of the control cir- cuitry. bypass ldo with a 1? capacitor to gnd. shutdown the max1908/max8724/max8765/MAX8765A feature a low-power shutdown mode. driving shdn low shuts down the max1908/max8724/max8765/MAX8765A. in shutdown, the dc-dc converter is disabled and cci, ccs, and ccv are pulled to ground. the iinp and acok outputs continue to function. shdn can be driven by a thermistor to allow automatic shutdown of the max1908/max8724/max8765/ MAX8765A when the battery pack is hot. the shutdown falling threshold is 23.5% (typ) of v refin with 1% v refin hysteresis to provide smooth shutdown when driven by a thermistor. dc-dc converter the max1908/max8724/max8765/MAX8765A employ a buck regulator with a bootstrapped nmos high-side switch and a low-side nmos synchronous rectifier. ccv, cci, ccs, and lvc control blocks the max1908/max8724/max8765/MAX8765A control input current (ccs control loop), charge current (cci control loop), or charge voltage (ccv control loop), depending on the operating condition. the three control loops, ccv, cci, and ccs are brought together internally at the lvc amplifier (lowest voltage clamp). the output of the lvc amplifier is the feedback control signal for the dc-dc controller. the output of the g m amplifier that is the lowest sets the output of the lvc amplifier and also clamps the other two control loops to within 0.3v above the control point. clamping the other two control loops close to the lowest control loop ensures fast transition with minimal overshoot when switching between different control loops. dc-dc controller the max1908/max8724/max8765/MAX8765A feature a variable off-time, cycle-by-cycle current-mode control scheme. depending upon the conditions, the max1908/ max8724/max8765 /MAX8765A work in continuous or discontinuous-conduction mode. continuous-conduction mode with sufficient charger loading, the max1908/max8724/ max8765/ MAX8765A operate in continuous-conduction mode (inductor current never reaches zero) switching at 400khz if the batt voltage is within the following range: 3.1v x (number of cells) < v batt < (0.88 x v dcin ) the operation of the dc-dc controller is controlled by the following four comparators as shown in figure 4: ? imin ?ompares the control point (lvc) against 0.15v (typ). if imin output is low, then a new cycle cannot begin. ? ccmp ?ompares the control point (lvc) against the charging current (csi). the high-side mosfet on- time is terminated if the ccmp output is high. ? imax ?ompares the charging current (csi) to 6a (rs2 = 0.015 ? ). the high-side mosfet on-time is terminated if the imax output is high and a new cycle cannot begin until imax goes low. ? zcmp ?ompares the charging current (csi) to 333ma (rs2 = 0.015 ? ). if zcmp output is high, then both mosfets are turned off. max1908/max8724/max8765/MAX8765A max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers 20 ______________________________________________________________________________________ imax reset 1.8v 0.15v 0.1v 5ms lvc control cells setv seti ccv cci ccs gms gmi gmv cls dlo dhi csi x20 t off generator bst s rq ccmp zcmp imin chg rq s css x20 cssp ac adapter cssn bst dhi lx rs1 ldo d3 n1a n1b c bst l1 rs2 dlo csip csin c out batt battery max1908 max8724 max8765 MAX8765A q cell select logic figure 4. dc-dc functional diagram dc-dc functional diagram max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers ______________________________________________________________________________________ 21 in normal operation, the controller starts a new cycle by turning on the high-side n-channel mosfet and turning off the low-side n-channel mosfet. when the charge current is greater than the control point (lvc), ccmp goes high and the off-time is started. the off-time turns off the high-side n-channel mosfet and turns on the low-side n-channel mosfet. the opera- tional frequency is governed by the off-time and is dependent upon v dcin and v batt . the off-time is set by the following equations: where: these equations result in fixed-frequency operation over the most common operating conditions. at the end of the fixed off-time, another cycle begins if the control point (lvc) is greater than 0.15v, imin = high, and the peak charge current is less than 6a (rs2 = 0.015 ? ), imax = high. if the charge current exceeds imax, the on-time is terminated by the imax compara- tor. imax governs the maximum cycle-by-cycle current limit and is internally set to 6a (rs2 = 0.015 ? ). imax protects against sudden overcurrent faults. if, during the off-time, the inductor current goes to zero, zcmp = high, both the high- and low-side mosfets are turned off until another cycle is ready to begin. there is a minimum 0.3? off-time when the (v dcin - v batt ) differential becomes too small. if v batt 0.88 v dcin , then the threshold for minimum off-time is reached and the t off is fixed at 0.3?. a maximum on- time of 5ms allows the controller to achieve > 99% duty cycle in continuous-conduction mode. the switching frequency in this mode varies according to the equation: discontinuous conduction the max1908/max8724/max8765/MAX8765A enter dis- continuous-conduction mode when the output of the lvc control point falls below 0.15v. for rs2 = 0.015 ? , this corresponds to 0.5a: for rs2 = 0.015 ? . in discontinuous mode, a new cycle is not started until the lvc voltage rises above 0.15v. discontinuous- mode operation can occur during conditioning charge of overdischarged battery packs, when the charge cur- rent has been reduced sufficiently by the ccs control loop, or when the battery pack is near full charge (con- stant-voltage-charging mode). mosfet drivers the low-side driver output dlo switches between pgnd and dlov. dlov is usually connected through a filter to ldo. the high-side driver output dhi is boot- strapped off lx and switches between v lx and v bst . when the low-side driver turns on, bst rises to one diode voltage below dlov. filter dlov with a lowpass filter whose cutoff frequency is approximately 5khz (figure 1): dropout operation the max1908/max8724/max8765/MAX8765A have 99% duty-cycle capability with a 5ms (max) on-time and 0.3? (min) off-time. this allows the charger to achieve dropout performance limited only by resistive losses in the dc-dc converter components (d1, n1, rs1, and rs2, figure 1). replacing diode d1 with a p-channel mosfet driven by acok improves dropout performance (figure 2). the dropout voltage is set by the difference between dcin and csin. when the dropout voltage falls below 100mv, the charger is disabled; 200mv hysteresis ensures that the charger does not turn back on until the dropout volt- age rises to 300mv. compensation each of the three regulation loops?nput current limit, charging current limit, and charging voltage limit?re compensated separately using ccs, cci, and ccv, respectively. f rc f khz c == = 1 2 1 2331 48 ? . imin v rs a = = 015 20 2 05 . . f li vv s ripple cssn batt = ? () + 1 03 . f tt on off = + 1 i vt l ripple batt off = t li vv on ripple cssn batt = ? ts vv v off dcin batt dcin = ? 25 . max1908/max8724/max8765/MAX8765A max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers 22 ______________________________________________________________________________________ ccv loop definitions compensation of the ccv loop depends on the para- meters and components shown in figure 5. c cv and r cv are the ccv loop compensation capacitor and series resistor. r esr is the equivalent series resistance (esr) of the charger output capacitor (c out ). r l is the equivalent charger output load, where r l = v batt / i chg . the equivalent output impedance of the gmv amplifier, r ogmv 10m ? . the voltage amplifier transconductance, gmv = 0.125?/mv. the dc-dc converter transconductance, gm out = 3.33a/v: where a csi = 20, and rs2 is the charging current- sense resistor in the typical application circuits . the compensation pole is given by: the compensation zero is given by: the output pole is given by: where r l varies with load according to r l = v batt /i chg. output zero due to output capacitor esr: the loop transfer function is given by: assuming the compensation pole is a very low frequency, and the output zero is a much higher fre- quency, the crossover frequency is given by: to calculate r cv and c cv values of the circuit of figure 2: cells = 4 c out = 22? v batt = 16.8v i chg = 2.5a gmv = 0.125?/mv gm out = 3.33a/v r ogmv = 10m ? f = 400khz choose crossover frequency to be 1/5th the max1908? 400khz switching frequency: solving yields r cv = 26k ? . conservatively set r cv = 1k ? , which sets the crossover frequency at: f co_cv = 3khz choose the output-capacitor esr so the output-capacitor zero is 10 times the crossover frequency: f rc mhz z esr esr out _ . = = 1 2 2 412 r fc esr co cv out = = 1 210 024 _ . ? f gmv r gm c khz co cv cv out out _ = = 2 80 f gmv r gm c co cv cv out out _ = 2 ltf gm r gmv r sc r sc r sc r sc r out l ogmv out esr cv cv cv ogmv out l = + () + () + () + () 11 11 f rc z esr esr out _ = 1 2 f rc p out l out _ = 1 2 f rc zcv cv cv _ = 1 2 f rc pcv ogmv cv _ = 1 2 gm ars out csi = 1 2 gm out batt ccv gmv ref r cv c cv r ogmv r esr r l c out figure 5. ccv loop diagram max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers ______________________________________________________________________________________ 23 the 22? ceramic capacitor has a typical esr of 0.003 ? , which sets the output zero at 2.412mhz. the output pole is set at: where: set the compensation zero (f z_cv ) so it is equivalent to the output pole (f p_out = 1.08khz), effectively produc- ing a pole-zero cancellation and maintaining a single- pole system response: choose c cv = 100nf, which sets the compensation zero (f z_cv ) at 1.6khz. this sets the compensation pole: cci loop definitions compensation of the cci loop depends on the parame- ters and components shown in figure 7. c ci is the cci loop compensation capacitor. a csi is the internal gain of the current-sense amplifier. rs2 is the charge cur- rent-sense resistor, rs2 = 15m ? . r ogmi is the equiva- lent output impedance of the gmi amplifier 10m ? . gmi is the charge-current amplifier transconductance = 1?/mv. gm out is the dc-dc converter transcon- ductance = 3.3a/v. the cci loop is a single-pole sys- tem with a dominant pole compensation set by f p_ci : the loop transfer function is given by: since: the loop transfer function simplifies to: ltf gmi r sr c ogmi ogmi ci = + 1 gm ars out csi = 1 2 ltf gm a rs gmi r sr c out csi ogmi ogmi ci = + 2 1 f rc pci ogmi ci _ = 1 2 f rc hz pcv ogmv cv _ . = = 1 2 016 c r khz nf cv cv = = 1 2108 147 . f rc zcv cv cv _ = 1 2 r v i battery esr l batt chg == ? ? f rc khz p out l out _ . = = 1 2 108 max1908/max8724/max8765/MAX8765A ccv loop gain vs. frequency frequency (hz) gain (db) 100k 10k 1k 100 10 -40 -20 0 20 40 60 80 -60 11m ccv loop phase vs. frequency frequency (hz) phase (degrees) 100k 10k 1k 100 10 -120 -105 -90 -75 -60 -45 -135 11m figure 6. ccv loop gain/phase vs. frequency max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers 24 ______________________________________________________________________________________ the crossover frequency is given by: the cci loop dominant compensation pole: where the gmi amplifier output impedance, r ogmi = 10m ? . to calculate the cci loop compensation pole, c ci : gmi = 1?/mv gm out = 3.33a/v r ogmi = 10m ? f = 400khz choose crossover frequency f co_ ci to be 1/5th the max1908/max8724/max8765/MAX8765A switching frequency: solving for c ci , c ci = 2nf. to be conservative, set c ci = 10nf, which sets the crossover frequency at: the compensation pole, f p_ci is set at: ccs loop definitions compensation of the ccs loop depends on the parame- ters and components shown in figure 9. c cs is the ccs loop compensation capacitor. a css is the internal gain of the current-sense amplifier. rs1 is the input current- sense resistor, rs1 = 10m ? . r ogms is the equivalent output impedance of the gms amplifier 10m ? . gms is f gmi rc hz pci ogmi ci _ . = = 2 0 0016 f gmi nf khz co ci _ == 210 16 f gmi c khz co ci ci _ == 2 80 f rc pci ogmi ci _ = 1 2 f gmi c co ci ci _ = 2 gm out cci gmi ictl c ci r ogmi csip csin csi rs2 figure 7. cci loop diagram cci loop gain vs. frequency frequency (hz) gain (db) 100k 10k 1 10 100 1k -40 -20 0 20 40 60 80 100 -60 0.1 1m cci loop phase vs. frequency frequency (hz) phase (degrees) 100k 10k 1k 100 10 1 -90 -75 -60 -45 -30 -15 0 -105 0.1 1m max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers ______________________________________________________________________________________ 25 the charge-current amplifier transconductance = 1?/mv. gm in is the dc-dc converter transconductance = 3.3a/v. the ccs loop is a single-pole system with a dom- inant pole compensation set by f p_cs : the loop transfer function is given by: since: then, the loop transfer function simplifies to: the crossover frequency is given by: the ccs loop dominant compensation pole: where the gms amplifier output impedance, r ogms = 10m ? . to calculate the cci loop compensation pole, c cs : gms = 1?/mv gm in = 3.33a/v r ogms = 10m ? f = 400khz f rc pcs ogms cs _ = 1 2 f gms c co cs cs _ = 2 ltf gms r sr c ogms ogms cs = + 1 gm ars in css = 1 1 ltf gm a rs gms r sr c in css ogms ogms cs = + 1 1 f rc pcs ogms cs _ = 1 2 max1908/max8724/max8765/MAX8765A gm in ccs gms cls c cs r ogms cssp cssn css rs1 figure 9. ccs loop diagram ccs loop gain vs. frequency frequency (hz) gain (db) 100k 10k 1 10 100 1k -40 -20 0 20 40 60 80 100 -60 0.1 1m ccs loop phase vs. frequency frequency (hz) phase (degrees) 100k 10k 1k 100 10 1 -90 -75 -60 -45 -30 -15 0 -105 0.1 1m figure 10. ccs loop gain/phase vs. frequency max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers 26 ______________________________________________________________________________________ choose crossover frequency f co_cs to be 1/5th the max1908/max8724/max8765/MAX8765A switching frequency: solving for c cs , c cs = 2nf. to be conservative, set c cs = 10nf, which sets the crossover frequency at: the compensation pole, f p_cs is set at: component selection table 3 lists the recommended components and refers to the circuit of figure 2. the following sections describe how to select these components. inductor selection inductor l1 provides power to the battery while it is being charged. it must have a saturation current of at least the charge current (i chg ), plus 1/2 the current rip- ple i ripple : i sat = i chg + (1/2) i ripple ripple current varies according to the equation: i ripple = (v batt ) t off /l where: t off = 2.5? (v dcin ?v batt )/v dcin v batt < 0.88 v dcin or: t off = 0.3? v batt > 0.88 v dcin figure 11 illustrates the variation of ripple current vs. battery voltage when charging at 3a with a fixed 19v input voltage. higher inductor values decrease the ripple current. smaller inductor values require higher saturation cur- rent capabilities and degrade efficiency. designs for ripple current, i ripple = 0.3 i chg usually result in a good balance between inductor size and efficiency. input capacitor input capacitor c1 must be able to handle the input ripple current. at high charging currents, the dc-dc converter operates in continuous conduction. in this case, the ripple current of the input capacitor can be approximated by the following equation: where: i c1 = input capacitor ripple current. d = dc-dc converter duty ratio. i chg = battery-charging current. input capacitor c1 must be sized to handle the maxi- mum ripple current that occurs during continuous con- duction. the maximum input ripple current occurs at 50% duty cycle; thus, the worst-case input ripple cur- rent is 0.5 i chg . if the input-to-output voltage ratio is such that the dc-dc converter does not operate at a 50% duty cycle, then the worst-case capacitor current occurs where the duty cycle is nearest 50%. the input capacitor esr times the input ripple current sets the ripple voltage at the input, and should not exceed 0.5v ripple. choose the esr of c1 according to: the input capacitor size should allow minimal output voltage sag at the highest switching frequency: i c dv dt c1 2 1 = esr v i c c 1 1 05 < . ii dd c chg 1 2 =? f rc hz pcs ogms cs _ . = = 1 2 0 0016 f gms nf khz co cs _ == 210 16 f gms c khz co cs cs _ == 2 80 ripple current vs. battery voltage v batt (v) ripple current (a) 14 13 12 11 10 9 0.5 1.0 1.5 0 8 15161718 v dcin = 19v vctl = ictl = ldo 4 cells 3 cells figure 11. ripple current vs. battery voltage max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers ______________________________________________________________________________________ 27 max1908/max8724/max8765/MAX8765A where dv is the maximum voltage sag of 0.5v while delivering energy to the inductor during the high-side mosfet on-time, and dt is the period at highest oper- ating frequency (400khz): both tantalum and ceramic capacitors are suitable in most applications. for equivalent size and voltage rating, tantalum capacitors have higher capacitance, but also higher esr than ceramic capacitors. this makes it more critical to consider ripple current and power-dissipation ratings when using tantalum capaci- tors. a single ceramic capacitor often can replace two tantalum capacitors in parallel. output capacitor the output capacitor absorbs the inductor ripple cur- rent. the output capacitor impedance must be signifi- cantly less than that of the battery to ensure that it absorbs the ripple current. both the capacitance and esr rating of the capacitor are important for its effec- tiveness as a filter and to ensure stability of the dc-dc converter (see the compensation section). either tanta- lum or ceramic capacitors can be used for the output filter capacitor. mosfets and diodes schottky diode d1 provides power to the load when the ac adapter is inserted. this diode must be able to deliver the maximum current as set by rs1. for reduced power dissipation and improved dropout per- formance, replace d1 with a p-channel mosfet (p1) as shown in figure 2. take caution not to exceed the maximum v gs of p1. choose resistors r11 and r12 to limit the v gs . the n-channel mosfets (n1a, n1b) are the switching devices for the buck controller. high-side switch n1a should have a current rating of at least the maximum charge current plus one-half the ripple current and have an on-resistance (r ds(on) ) that meets the power dissipation requirements of the mosfet. the driver for n1a is powered by bst. the gate-drive requirement for n1a should be less than 10ma. select a mosfet with a low total gate charge (q gate ) and determine the required drive current by i gate = q gate f (where f is the dc-dc converter? maximum switching frequency). the low-side switch (n1b) has the same current rating and power dissipation requirements as n1a, and should have a total gate charge less than 10nc. n2 is used to provide the starting charge to the bst capacitor (c15). during the dead time (50ns, typ) between n1a and n1b, the current is carried by the body diode of the mosfet. choose n1b with either an internal schottky diode or body diode capable of carrying the maximum charging current during the dead time. the schottky diode d3 provides the supply current to the high-side mosfet driver. layout and bypassing bypass dcin with a 1? capacitor to power ground (figure 1). d2 protects the max1908/max8724/ max8765/MAX8765A when the dc power source input is reversed. a signal diode for d2 is adequate because dcin only powers the internal circuitry. bypass ldo, ref, ccv, cci, ccs, ichg, and iinp to analog ground. bypass dlov to power ground. good pc board layout is required to achieve specified noise, efficiency, and stable performance. the pc board layout artist must be given explicit instructions preferably, a pencil sketch showing the placement of the power-switching components and high-current rout- ing. refer to the pc board layout in the max1908 eval- uation kit for examples. separate analog and power grounds are essential for optimum performance. use the following step-by-step guide: 1) place the high-power connections first, with their grounds adjacent: a) minimize the current-sense resistor trace lengths, and ensure accurate current sensing with kelvin connections. b) minimize ground trace lengths in the high-current paths. c) minimize other trace lengths in the high-current paths. d) use > 5mm wide traces. e) connect c1 to high-side mosfet (10mm max length). f) lx node (mosfets, inductor (15mm max length)). ideally, surface-mount power components are flush against one another with their ground terminals almost touching. these high-current grounds are then connected to each other with a wide, filled zone of top-layer copper, so they do not go through vias. the resulting top-layer power ground plane is connected to the normal ground plane at the max1908/max8724/max8765/MAX8765As?back- side exposed pad. other high-current paths should also be minimized, but focusing primarily on short ground and current-sense connections eliminates most pc board layout problems. c i s v c 1 2 25 05 1 > . . max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers 28 ______________________________________________________________________________________ table 3. component list for circuit of figure 2 designation qty description c1 2 10?, 50v 2220-size ceramic capacitors tdk c5750x7r1h106m c4 1 22?, 25v 2220-size ceramic capacitor tdk c5750x7r1e226m c5 1 1?, 25v x7r ceramic capacitor (1206) murata grm31mr71e105k taiyo yuden tmk316bj105kl tdk c3216x7r1e105k c9, c10 2 0.01?, 16v cer am i c cap aci tor s ( 0402) murata grp155r71e103k taiyo yuden emk105bj103kv tdk c1005x7r1e103k c11, c14, c15, c20 4 0.1?, 25v x7r ceramic capacitors (0603) murata grm188r71e104k tdk c1608x7r1e104k c12, c13, c16 3 1?, 6.3v x5r ceramic capacitors (0603) murata grm188r60j105k taiyo yuden jmk107bj105ka tdk c1608x5r1a105k d1 (optional) 1 10a schottky diode (d-pak) diodes, inc. mbrd1035ctl on semiconductor mbrd1035ctl d2 1 schottky diode central semiconductor cmpsh1? designation qty description d3 1 schottky diode central semiconductor cmpsh1-4 l1 1 10?, 4.4a inductor sumida cdrh104r-100nc toko 919as-100m n1 1 dual, n-channel, 8-pin so mosfet fairchild fds6990a or fds6990s p1 1 single, p-channel, 8-pin so mosfet fairchild fds6675 r5 1 1k ? ?% resistor (0603) r6 1 59k ? ?% resistor (0603) r7 1 19.6k ? ?% resistor (0603) r11 1 12k ? ?% resistor (0603) r12 1 15k ? ?% resistor (0603) r13 1 33 ? ?% resistor (0603) r14 1 10.5k ? ?% resistor (0603) r15, r16 2 8.25k ? ?% resistors (0603) r17 1 19.1k ? ?% resistor (0603) r18 1 22k ? ?% resistor (0603) r19, r20 2 10k ? ?% resistors (0603) rs1 1 0.01 ? ?%, 0.5w 2010 sense resistor vishay dale wsl2010 0.010 1.0% irc lrc-lr2010-01-r010-f rs2 1 0.015 ? ?%, 0.5w 2010 sense resistor vishay dale wsl2010 0.015 1.0% irc lrc-lr2010-01-r015-f u1 1 max1908eti+, max8724eti+, or max8765eti+, MAX8765Aeti+ 2) place the ic and signal components. keep the main switching node (lx node) away from sensitive analog components (current-sense traces and ref capacitor). important: the ic must be no further than 10mm from the current-sense resistors. keep the gate-drive traces (dhi, dlo, and bst) shorter than 20mm, and route them away from the current-sense lines and ref. place ceramic bypass capacitors close to the ic. the bulk capac- itors can be placed further away. 3) use a single-point star ground placed directly below the part at the backside exposed pad of the max1908/max8724/max8765/MAX8765A. connect the power ground and normal ground to this node. max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers ______________________________________________________________________________________ 29 chip information transistor count: 3772 process: bicmos package information for the latest package outline information and land patterns, go to www.maxim-ic.com/packages . note that a "+", "#", or "-" in the package code indicates rohs status only. package draw- ings may show a different suffix character, but the drawing per- tains to the package regardless of rohs status. package type package code document no. 28 tqfn-ep t2855-6 21-0140 max1908/max8724/max8765/MAX8765A low-cost multichemistry battery chargers maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. 30 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 2009 maxim integrated products maxim is a registered trademark of maxim integrated products, inc. revision history revision number revision date description pages changed 0 2/03 initial release 5 11/09 added the MAX8765A to the data sheet. 1?0 |
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