249 www.ptcc.com.tw AS2916 pwm controller semiconductor features dual pwm controller ultra low start-up current, less than 25 a main converter soft-start frequency randomizer for improved emi performance bulk detect circuitry remote on/off control buffered ramp for slope compensation optional auxiliary converter primary regulation high main converter drive capability undervoltage lockout circuitry accurate reference standard temperature range extended to 105? description the AS2916 is a dual, full featured, pulse width modulation controller. the second controller is intended to run the auxiliary supply. both con- trollers share common oscillator and power up logic. based on an improved as3842, the AS2916 provides additional features that reduce component count and improve specifications in a wide range of power supply designs. the added functionality also includes bulk voltage sensing, overvoltage input and soft-start. the pwm function is controlled by the current sense comparator for normal current mode control and a second comparator for voltage mode soft-start. a buffered ramp signal is available for slope compensation without loading the oscillator. the output stage is a high current totem pole output that sees only 140 ns delay from the pwm comparators. the AS2916 requires less than 25 a of startup current. the under- voltage lockout (uvlo) thresholds are nominally 13.5 v for turn-on and 7.5 v for turn-off. the oscillator discharge current is trimmed to provide guaranteed duty cycle clamping. the AS2916 has a second low fre- quency oscillator, which frequency modulates the operating frequency of the pwm by 25%, thus reducing emi emissions. pin configuration ? top view pgnd outa bok cmpa outb v cc reg snsb ramp osc gnd snsa cmpb ss outb v cc reg snsb ramp osc cmpb ss on wbl pgnd outa bok cmpa gnd snsa on wbl 16l pdip (16n) 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 16l soic (16d) 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 circuit type: pwm controller temperature range: b = 0 c to 105 c packaging option: t = tubes n = tape and reel (13" reel dia) package style: 16d = 16 pin, plastic soic 16n = 16 pin, plastic dip AS2916 b 16d n ordering information
250 www.ptcc.com.tw AS2916 pwm controller 5v reg 5v enable snsb + reg v cc uvlo aux_on + + + + gnd outb outa gnd 50 a v reg x1 x1 gm 2v5 2v5 bok on cmpb wbl rt/ct ramp cmpa snsa + ss 6 a v reg osc osc 2r 2r 1v r 1v r (pwm) ss pwm (pwm) v cc v cc v cc (blank) (blank) aux_on cm pwm cm pwm s r q (bulk ok) (run) functional block diagram
251 www.ptcc.com.tw AS2916 pwm controller pin function description pin number function description 1 outb this is the gate drive output for the main fet. the totem pole output has equivalent of an extra 10 ? resistor to limit the fet turn on speed and a pull down resistor to ensure the fet gate is never open. no external circuitry except for the fet is expected on this pin. the largest fet expected to be driven is irfbc40. if a larger power fet is used, a buffer might be required. 2v cc positive supply for the ic. absolute maximum rating is 20 v. the running voltage shall be provided by the auxiliary conver tor. 3 reg output of 5 v series regulator. 4 snsb this is the main convertor current sense pin. an external rc filter from the main power fet and slope compensation resis- tor from the ramp pin is all the expected external circuitry. 5 cmpb this is the main output control pin. an opto isolated control signal from the secondary side error amplifier is buffered and connected to the invert pin of the main output current mode comparator. a pull-up current of 1 ma is provided so the only external circuitry expected is a common emitter opto-isolator. 6 ss this pin provides a 6 a current source to linearly charge an external capacitor. this spin is compared to the ramp pin in the soft start comparator, terminating output pulses when ramp goes above the ss voltage. while this pin is held low, the main output is inhibited. 7 ramp this pin is a level-shifted and buffered oscillator waveform, used to provide slope compensation for the main and auxiliary converters. the pin also serves as the non-inverting input of the soft-start comparator. 8 osc oscillator frequency and maximum duty cycle are set by con- necting the resistor (r t ) to v reg and a capacitor (c t ) to ground. 9 wbl provides an fm modulation of the oscillator, approximately 25% deviation frequency, at a modulation rate set by an exter- nal cap at wbl. shorting to gnd eliminates modulation. 10 on this pin is used to remotely turn the main convertor on/off either for normal user application or for protection. 11 bok bulk ok. this is a brownout protection feature. the pin moni- tors the bulk voltage through a resistor divider. when bok exceeds 2.5 v a 50 a current is sourced from the pin for hys- teresis. when the pin drops below 2.5 v the hysteresis is turned off and ss is pulled low,inhibiting the main output. the auxiliary output is not tied to bok and will run as long as there is sufficient bias voltage.
252 www.ptcc.com.tw AS2916 pwm controller pin function description pin number function description 12 cmpa this is the auxiliary convertor error amplifier compensation pin or if secondary controller is desired, the auxiliary control input pin. a simple capacitor to ground is the only circuitry expected. note: there is no external connection for voltage feedback. voltage sensing is provided internally in such a way that v cc is not loaded until it reaches predefined threshold. if secondary control is required, it can be forced into the cmpa pin. 13 snsa this is the auxiliary convertor current sense pin. an external rc filter from the auxiliary power fet and slope compensation resistor from the ramp pin is all the expected external cir- cuitry. 14 outa this is the gate drive output for the auxiliary fet. the totem pole output has equivalent of an extra 33 ? resistor to limit the fet turn on speed and a pull down resistor to ensure the fet gate is never open. no external circuitry except for the fet is expected on this pin. the largest fet expected to be driven is irf820. if a larger power fet is used, a buffer might be required. 15 gnd signal ground. 16 pgnd power ground. absolute maximum ratings parameter symbol rating unit reference current i ref 200 ma output current i out 1a supply voltage v cc 20 v output voltage v out 20 v continuous power p d 500 mw junction temperature t j 150 ? storage temperature t stg ?0 to +150 ? lead temperature (soldering, 10 seconds) t l 300 ?
253 www.ptcc.com.tw AS2916 pwm controller electrical characteristics electrical characteristics are guaranteed over the full junction temperature range (0-105?. ambient temperature must be derat ed based upon power dissipation and package thermal characteristics. the conditions are: v cc = 15 v, bok = 3 v, on = 3 v, r t = 680 ? , c t = 10 nf, and c wbl = 2.2 nf, unless otherwise specified. to override uvlo, v cc should be raised above uvlo high prior to test. parameter symbol test condition min. typ. max. unit 5 v regulator output voltage v reg t j = 25?, i reg = 1 ma 4.90 5.00 5.10 v line regulation psrr 12 v cc 18 v 5 15 mv load regulation 1.0 i reg 20 ma 5 15 mv temperature stability tc reg 0.2 0.4 mv/? total output variation line, load, temperature 4.85 5.15 v long-term stability over 1,000 hrs at 25? 5.0 25 mv output noise voltage v noise 10 f 100 khz, t j = 25? 50 v maximum source current i max vreg = 4.8 v 30 120 180 ma oscillator initial frequency f osc t a = 25?, v wbl = 0 v 117 132 143 khz voltage stability 8.5 v v cc 18v 0.2 1.0 % temperature stability tc f t min t j t max 5% amplitude v osc v osc peak-to-peak 1.55 v upper trip point v h v wbl = 0 v 2.8 v lower trip point v l v wbl = 0 v 1.25 v discharge current i dsc v osc = 3 v 7.5 8.7 9.5 ma duty cycle limit r t = 680 ? , c t = 10 nf, 46 50 54 % t j = 25? over-temperature shutdown t ot 140 ? wobble oscillator wobble rate f wbl 2.2 nf wbl to gnd 3.4 4.5 6.0 khz osc frequency deviation dev change in main oscillator freq. +30 +40 +50 khz amplitude v wbl v wbl peak-to-peak 1.8 v upper trip point v h 2.7 v lower trip point v l 0.9 v charge current i chrg v wbl = 0.7 v ?5 ?6 ?0 a discharge current i dsc v wbl = 4.8 v 25 36 50 a
254 www.ptcc.com.tw AS2916 pwm controller electrical characteristics electrical characteristics are guaranteed over the full junction temperature range (0-105?. ambient temperature must be derat ed based upon power dissipation and package thermal characteristics. the conditions are: v cc = 15 v, bok = 3 v, on = 3 v, r t = 680 ? , c t = 10 nf, and c wbl = 2.2 nf, unless otherwise specified. to override uvlo, v cc should be raised above uvlo high prior to test. parameter symbol test condition min. typ. max. unit auxiliary pwm comparator input (cmpa) regulation voltage v ccreg 13.4 14.5 15.7 v transconductance g m 1.0 ms output sink current i cmpalow v cc = 16 v, v cmpa = 1.1 v 2.0 6.0 ma output source current i cmpahigh v cc = 12 v, v cmpa = 5 v ?.5 -1.1 ma output swing high v cmpahigh v cc = 12 v, i cmpa = 0.5 ma 5.4 5.7 v output swing low v cmpalow v cc = 16 v, i cmpa = 2 ma 0.2 1.1 v auxiliary current sense comparator (snsa) transfer gain a vsnsa ?.2 v snsa 0.8 v 3.0 v/v cmpa level shift v ls v snsa = 0 v 1.5 v current sense threshold v snsa v cmpa = 5 v 0.95 1.05 1.15 v input bias current i bias ?.0 ?0 a propagation delay to output t pd 80 150 ns main pwm comparator input (cmpb) comp source current i cmpb v cmpb = 2.5 v ?.0 ?.4 ma comp source impedance z cmpb 10 15 20 k ? comp source high v cmpbhigh 5.4 5.6 v main current sense comparator (snsb) transfer gain a vsnsb ?.2 v snsb 0.8 v 3.0 v/v cmpb level shift v ls v snsb = 0 v 1.5 v current sense threshold v snsb v cmpb = 5 v 0.95 1.05 1.15 v input bias current i bias ?.0 ?0 a propagation delay to output t pd 80 150 ns soft start comparator ss charge current i charge ss v ss v ramp ?.0 ?.0 ?0 a ss discharge current i dsc ss v ss = 1 v, v on <1.5 v 2.0 10 ma ss lower clamp v ss low 0.05 0.2 v propagation delay to output t pb 50 100 ns ramp high level v ramph t j = 25? 2.0 2.15 2.3 v ramp low level v rampl t j = 25? 0.45 0.6 0.75 v ramp levels t c note: ramp waveform is same ?.0 mv/? as osc waveform, but level shifted down one diode drop. ramp sink current i rampl t j = 25? 0.1 0.2 ma ramp source current i ramph t j = 25? ?.0 ?0 ma
255 www.ptcc.com.tw AS2916 pwm comtroller electrical characteristics electrical characteristics are guaranteed over the full junction temperature range (0-105?. ambient temperature must be derat ed based upon power dissipation and package thermal characteristics. the conditions are: v cc = 15 v, bok = 3 v, on = 3 v, r t = 680 ? , c t = 10 nf, and c wbl = 2.2 nf ,unless otherwise specified. to override uvlo, v cc should be raised above uvlo high prior to test. parameter symbol test condition min. typ. max. unit main output output low level v outbl i sink = 10 ma 0.1 0.4 v output low level v outbl i sink = 150 ma 1.5 2.2 v output high level v outbh i source = 10 ma, v cc = 15 v 12 13 v output high level v outbh i source = 150 ma, v cc = 15v 10 10.7 v on resistance high 10 ? rise time t r c l = 1.3 nf, 10% to 90% 50 150 ns fall time t f c l = 1.3 nf, 90% to 10% 50 150 ns output impedance to gnd z out vcc = 6 v 20 k ? in uvlo state auxiliary output output low level v outbl i sink = 10 ma 0.1 0.4 v output low level v outbl i sink = 150 ma 1.5 2.2 v output high level v outbh i source = 10 ma, v cc = 15v, 12 13 v v cmpa = 5 v output high level v outbh i source = 110 ma, v cc = 15v, 7 8 v v cmpa = 5 v on resistance high 33 ? rise time t r c l =350 pf, 10% to 90% 70 150 ns fall time t f c l = 350 pf, 90% to 10% 50 150 ns output impedance to gnd z out v cc = 6 v 20 k ? in uvlo state under-voltage lockout start-up threshold v cc(on) 12.4 13.5 14.7 v stop threshold v cc(off) 7 7.5 8 v start-up current i cc 0.1 25 a operating supply current i cc v cc = 15 v 18 25 ma housekeeping bok uv threshold v bok uv t j = 25? 2.50 2.537 2.575 v bok uv hysteresis current i hyst bok v bok = 2.6 v 42 50 58 a bok input bias current i bok v bok = 2.4 v 0.1 1.0 a on threshold v on 2.35 2.5 2.65 v on hysteresis ? v on ?.7 ?.9 ?.1 v on bias current i bias on v on = 2.3 v 0.5 ?0 a
256 www.ptcc.com.tw
|
