si9121 vishay siliconix document number: 71112 s-40708?rev. c, 19-apr-04 www.vishay.com 1 high-voltage, non-isolated buck-boost converter for isdn digital phones features fixed +5-v or +3.3-v output integrated floating feedback amplifier on-chip 70-v, 1.5- n-channel mosfet switch integrated high voltage start-up circuit, with v cc regulator ? 10-v to ? 60-v input voltage range 95-khz pwm operation integrated soft-start and oscillator high efficiency over full load range under voltage lockout current mode control hiccup mode short circuit protection thermal shutdown soic-8 narrow-body package description the si9121 simplifies the ? 48-v to +5-v or +3.3-v converter design for isdn application by integrating the floating feedback error amplifier providing direct output voltage regulation. this approach eliminates the need for an external shunt regulator. the si9121 also integrates a high voltage depletion mode mosfet which allows the converter to be powered directly from the high input bus voltage without requiring an external start-up circuit. combined with simple magnetic design due to its non-isolated topology, the si9121 provides a one-chip solution for complete isdn power supply. in order to reduce external component count, the si9121 has a fully integrated 95-khz oscillator and soft-start circuit. the si9121 is available in both standard and lead (pb)-free soic-8 pin packages, and is offered in either +5-v or +3.3-v fixed output options (si9121dy-5 or si9121dy-3, respectively). in order to satisfy the stringent ambient temperature requirements in many applications, the si9121 is rated to the industrial temperature range of ? 40 c to 85 c. functional block diagram v neg ? 48 v v out +5 v/400 ma or +3.3 v/400 ma v cc regulator reference generator control v cc l x bypass comp v neg c s v out gnd
si9121 vishay siliconix www.vishay.com 2 document number: 71112 s-40708?rev. c, 19-apr-04 absolute maximum ratings (all voltages referenced to gnd = 0 v) v neg ? 63 v . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v cs v neg ? 0.3 v to v cc + 0.3 v . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v cc v neg + 13.2 v . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i lx (peak current ) 3 a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v out 6 v . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . bypass, cs v neg ? 0.3 v to v cc +0.3 v . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (v lx ? v cs ) internal power mosfet 70 v . . . . . . . . . . . . . . . . . . . . . . . . . . . . storage temperature ? 65 to 150 c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . operating junction temperature 150 c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . power dissipation (package) a 8-pin soic (y suffix) b 1.25 w . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . thermal impedance ( ja ) a 8-pin soic 100 c/w . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . notes a. device mounted with all leads soldered or welded to pc board. b. derate 10 mw/ c above 25 c. stresses beyond those listed under ?absolute maximum ratings? may cause permanent damage to the device. these are stress ratin gs 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. recommended operating range (all voltages referenced to gnd = 0 v) v neg ? 10 v to ? 60 v . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v cc (internally regulated) v neg + 8.5 v . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v cc (externally supplied) v neg + 9.5 v to v neg + 12.0 v . . . . . . . . . . . . . . . . digital inputs 0 v to v cc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . recommended external components ( see typical applications circuit ) l = 68 h, c out = 220 f // 0.1 f, cin = 33 f, c bypass = 0.1 f, c vcc = 1 f, r sense = 0.25 , 0.5 w specifications a (all voltages are with respect to v neg unless otherwise specified) test conditions (internally regulated) unless otherwise specified limits ? 40 to 85 c parameter symbol p v neg = ? 10 to ? 60 v temp b min c typ d max c unit output voltage (with respect to gnd = 0 v) +5-v converter v out 10 ma si9121 vishay siliconix document number: 71112 s-40708?rev. c, 19-apr-04 www.vishay.com 3 specifications a (all voltages are with respect to v neg unless otherwise specified) test conditions (internally regulated) unless otherwise specified limits ? 40 to 85 c parameter symbol p v neg = ? 10 to ? 60 v temp b min c typ d max c unit supply supply current (internally regulater) i gnd gnd to v neg full 1.2 1.5 supply current (external v cc applied) i cc v cc to v neg +10 v; v neg > ? 20 v full 1.5 2.0 ma v out supply current i out v out to v neg full 0.2 0.3 start-up current i start v cc = 0 v full 5 30 thermal shutdown thermal shutdown temperature t otp 170 c thermal hysteresis t hys 25 c efficiency efficiency 400 ma output v neg = 48 v +5 v room 77 % efficiency 400-ma output, v neg = ? 48 v +3.3 v room 73 % notes a. refer to process option flowchart for additional information. b. room = 25 c, full = as determined by the operating temperature suffix. c. the algebraic convention whereby the most negative value is a minimum and the most positive a maximum. d. typical values are for design aid only, not guaranteed nor subject to production testing. detailed block diagram bypass r1* r2* v out ? + v ref 1.25 v + ? 0.6 v ? + pwm + ? 0.67 v osc r s q l x cs ? v in bias/ reference circuit v neg ? + v cc ? + 0.6-v hysteresis 50% max. duty cycle low side error amp ? + 8.5 v *r1 and r2 are internal voltage setting resistors used to set output voltage to fixed 3.3 v or 5 v. 5 3 2 7 8 1 ? + gm gnd 6 ocl otp comp 4 + ? 3.5 v ? + 1.5 v h l 10 a v cc 2 a v neg soft start hiccup discharge mode
si9121 vishay siliconix www.vishay.com 4 document number: 71112 s-40708?rev. c, 19-apr-04 typical characteristics (internally regulated, 25 c unless noted) 4.85 4.90 4.95 5.00 5.05 5.10 5.15 ? 40 ? 20 0 20 40 60 80 100 5-v v out vs. t emperature temperature ( c) (v) v out 0.5 1.0 1.5 2.0 2.5 ? 40 ? 20 0 20 40 60 80 100 r ds(on) vs. t emperature 1.0 1.1 1.2 1.3 1.4 ? 60 ? 50 ? 40 ? 30 ? 20 ? 10 supply current vs. v neg v neg ? (v) supply current (i 3.15 3.20 3.25 3.30 3.35 3.40 3.45 ? 40 ? 20 0 20 40 60 80 100 3.3-v v out vs. t emperature temperature ( c) (v) v out ? on-resistance ( r ds(on) ) temperature ( c) 85 90 95 100 105 ? 40 ? 20 0 20 40 60 80 100 frequency vs. t emperature frequency (khz) temperature ( c) gnd ) 25 c 85 c ? 40 c
si9121 vishay siliconix document number: 71112 s-40708?rev. c, 19-apr-04 www.vishay.com 5 typical characteristics (internally regulated, 25 c unless noted) 0 10 20 30 40 50 60 70 80 90 10 100 1000 0 10 20 30 40 50 60 70 80 90 10 100 1000 0 10 20 30 40 50 60 70 80 90 10 100 1000 output load vs. efficiency (si9121dy-3) no v cc winding output load vs. efficiency (si9121dy-5) no v cc winding output load vs. efficiency (si9121dy-3) with v cc winding i out (ma) efficiency (%) output load vs. efficiency (si9121dy-5) with v cc winding v neg = ? 60 v v neg = ? 10 v efficiency (%) v in = 48 v i out (ma) efficiency (%) 48 v in 10 v in 60 v in i out (ma) efficiency (%) 48 v in 10 v in 60 v in v neg = ? 48 v i out (ma) 0 10 20 30 40 50 60 70 80 90 10 100 1000 v in = 10 v v in = 60 v
soic-8 si9121 cs l x v neg v cc bypass gnd comp v out 5 6 7 8 top view 2 3 4 1 si9121 vishay siliconix www.vishay.com 6 document number: 71112 s-40708?rev. c, 19-apr-04 pin configuration and ordering information ordering information part number temperature range package si9121dy-5-t1 si9121dy-5-t1?e3 tape and reel si9121dy-3-t1 40 to 85 c tape and reel si9121dy-3-t1?e3 ? 40 to 85 c si9121dy-5 bulk si9121dy-3 bulk eval kit temperature range board type si9121db-5 10 to 70 c surface mount and si9121db-3 ? 10 to 70 c surface mount and thru-hole pin description pin number name function 1 cs current sense pin to detect the inductor current for current mode control and over current protection 2 v neg negative supply voltage ( ? 10 v to ? 60 v) 3 bypass +1.5-v bandgap reference. decouple with 0.1 f capacitor. 4 comp compensation node to stabilize the converter 5 v out output voltage feedback connected to the pwm summing comparator 6 gnd low impedance system ground 7 v cc internally generated supply voltage for the internal circuit and mosfet drive circuit. decouple with an external bypass capacitor. 8 l x inductor connection node detailed description start-up the uvlo circuit prevents the internal circuits from turning on if vcc is less than 7.6 v (typical) above the negative supply voltage at v neg pin. with a typical hysteresis of 0.6 v, the controller is continuously powered on until the v cc voltage drops below 7.0 v. this hysteresis prevents the converter from oscillating during the start-up phase and unintentionally locking up the system. once (v cc ? v neg ) exceeds the uvlo threshold the internal reference, oscillator, and soft-start circuits are enabled. soft-start the si9121 has an on-chip soft-start circuit which utilizes the error amplifier external compensation network to ramp the output nmos transistor current limit which, in turn, allows the output voltage to rise gradually without excessive overshoot. the soft-start circuit is enable once the v cc voltage exceeds the uvlo threshold. for the recommended frequency compensation components (see typical application circuit) the soft-start time is approximately 10 ms. oscillator the oscillator is designed to operate at a nominal frequency of 95 khz with no external components. the 95-khz operating frequency allows the converter to operate in pwm mode during the full load condition even though the d uty cycle is very low. the 95khz switching frequency also allows the converter to operate at optimal efficiency without a large output inductor and capacitor. pwm mode and current limit the si9121 is a current-mode converter designed to operate in pwm mode. it features pulse-by-pulse peak current limiting such that when the peak current sensed voltage on the cs pin is greater than 0.67 v the switch is turned off for the remainder of the clock cycle.
si9121 vishay siliconix document number: 71112 s-40708?rev. c, 19-apr-04 www.vishay.com 7 detailed description bypass the bypass voltage of the si9121 is set at a particular positive reference relative to the v neg pin. the bypass voltage is used to set an accurate voltage and bias current for the on-chip oscillator and soft-start circuits. the 0.1- f ceramic decoupling capacitor is recommended between the bypass and v neg . no other components should be connected to this pin. error amplifier with a ? 48-v bus voltage, the converter is referenced to the ? 48-v (v neg ) node as its system ground. however, the +5-v or +3.3-v output is referenced to the gnd pin, which is normally connected to 0 v. to regulate this output voltage, the si9121 has an on-chip error amplifier which continuously monitors the output voltage and compares it to a reference voltage. this difference signal is level-shifted to the low side circuit to control the power switch duty-cycle and hence the regulation of the output voltage. frequency compensation for the error amplifier is achieved by connecting an external network between the comp pin and the v neg pin. v cc regulator v cc is an internally generated bias supply voltage which should be externally bypassed with a 0.1- f capacitor connected to the negative supply voltage, v neg . no load current should be drawn from the v cc pin. v cc may be supplied from an external source of 9.5-v to 12-v referenced to v neg . in this configuration, the internal v cc regulator is disabled when the v cc receives 9.5-v, or greater, above v neg . thermal shutdown the si9121 also includes thermal shutdown which shuts down the device when junction temperature exceeds 170 c due to over heating. in thermal shutdown once the die temperature cools to below 145 c the regulator is enabled. if the die temperature is excessive due to high package power dissipation the regulator?s thermal circuit will continue to pulse the regulator on and off. this is called thermal cycling. hiccup mode short circuit protection in addition to the thermal shutdown and the cycle-by-cycle current limiting features already described, the si9121 has a built-in hiccup mode timer to handle a continuous output short-circuit and to automatically restart the device when the short-circuit is removed. if an output short-circuit occurs, the device immediately enters a cycle-by-cycle current limiting mode. as long as the thermal shutdown is not activated then the si9121 automatically determines whether the internal hiccup timer should be started by monitoring the comp pin. if v comp exceeds an upper threshold voltage (approximately 3.5 v) the timer is started and the external network at the comp pin is discharged by an internal 2- a current sink until v comp reaches approximately 1.5 v. (note: all voltages are with respect to v neg ). at this point, the circuit reverts to the normal soft-start mode, whereby the comp network is charged by its internal soft-start 10- a current source and the circuit will attempt to start up in the normal manner. however, if the output short circuit is still present, the converter will again enter the cycle-by-cycle current limiting mode until the comp pin voltage reaches 3.5 v, whereupon this cycle repeats until the short circuit is removed. the duty cycle imposed by the hiccup timer allows the si9121 to handle continuous short-circuit without damage as long as the recommended component values shown in the typical application circuit are used. mosfet switch the low-side n-channel mosfet switch is integrated to provide optimum performance and to minimize the overall converter size. the typical 1.5- r ds(on) of the mosfet allows the converter to deliver up to 2 w of output power.
si9121 vishay siliconix www.vishay.com 8 document number: 71112 s-40708?rev. c, 19-apr-04 typical application circuit bypass v cc v neg l x gnd v out comp cs 1 f c6 0.1 f c5* 33 f 80 v c4 r1 0.25 1 / 2 w 180 pf c7 220 f c2 0.1 f* c3 gnd v neg v out +5 v/400 ma or +3.3 v/400 ma l1 68 h + + 10mq100n 0.1 f c1 r2 75 k (27 k for si9121dy-3) 0.1 f c8 + si9121dy-5 or si9121dy-3 6 3 7 2 8 5 4 1 figure 1. typical applications circuit *optional ? 10 to ? 60 v silk screen v neg bypass comp coil cs v cc gnd v out + si9121dy-5 1 2 3 4 8 7 6 5 figure 2. si9121 application with external vcc through winding r1 0.25 1 / 2 w c3 0.1 f c4 180 pf gnd ? v in ? 10 to ? 60 v c1 33 f 80 v c5 0.1 f r2 75 k (27 k for si9121dy-3) c2* 0.1 f gnd +v out +5 v @ 400 ma c8* 0.1 f c7 220 f 10 v + d1 10mq100n ns t1 68 h np d2 bas21 c6 1 f *optional
legal disclaimer notice vishay document number: 91000 www.vishay.com revision: 08-apr-05 1 notice specifications of the products displayed herein are subjec t to change without notice. vishay intertechnology, inc., or anyone on its behalf, assume s no responsibility or liability fo r any errors or inaccuracies. information contained herein is intended to provide a product description only. no license, express or implied, by estoppel or otherwise, to any intellectual property rights is granted by this document. except as provided in vishay's terms and conditions of sale for such products, vishay assumes no liability whatsoever, and disclaims any express or implied warranty, relating to sale and /or use of vishay products including liab ility or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyrigh t, or other intellectual property right. the products shown herein are not designed for use in medical, life-saving, or life-sustaining applications. customers using or selling these products for use in such applications do so at their own risk and agree to fully indemnify vishay for any damages resulting from such improper use or sale.
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