unisonic technologies co., ltd UC3842A/3843a linear integrated circuit www.unisonic.com.tw 1 of 9 copyright ? 2011 unisonic technologies co., ltd qw-r103-002.f current mode pwm control circuits ? description the utc UC3842A/3843a provide the necessary functions to implement off-line or dc to dc fixed frequency current mode , controlled switching circuits with minimal external components. ? features *low start up current ( typical 0.12ma ) *automatic feed forward compensation *pulse-by-pulse current limiting *under-voltage lockout with hysteresis *double pulse suppression *high current totem pole out put to drive mosfet directly *internally trimmed band gap reference *500khz operation ? ordering information ordering number lead free halogen free package packing UC3842Al-d08-t UC3842Ap-d08-t dip-8 tube UC3842Al-s08-r UC3842Ap-s08-r sop-8 tape reel UC3842Al-s08-t UC3842Ap-s08-t sop-8 tube uc3843al-d08-t uc3843ap-d08-t dip-8 tube uc3843al-s08-r uc3843ap-s08-r sop-8 tape reel uc3843al-s08-t uc3843ap-s08-t sop-8 tube
UC3842A/3843a linear integrated circuit unisonic technologies co., ltd 2 of 9 www.unisonic.com.tw qw-r103-002.f ? pin configuration rt/ct output gnd 1 2 3 4 8 7 5 6 current sense comp v fb v ref v cc ? block diagram
UC3842A/3843a linear integrated circuit unisonic technologies co., ltd 3 of 9 www.unisonic.com.tw qw-r103-002.f ? absolute maximum ratings (ta=25 , unless otherwise specified) parameter symbol ratings unit supply voltage(low impedance source) v cc 30 v supply voltage(i cc <30ma) v cc self limiting v analog inputs(pin 2,3) v i(ana) -0.3 ~ +6.3 v output current ( peak ) i o(peak) 1 a error amplifier output sink current i sink(ea) 10 ma output energy (capacity load) 5 j dip-8 1.0 w power dissipation( ta Q 25 c) sop-8 0.5 w derated at ta>25 c p d 8 mw/ c junction temperature t j +150 c storage temperature t stg -65 ~ +150 c note absolute maximum ratings are those values beyond which the device which the device could be permanently damaged. absolute maximum ratings are stress ratings on ly and functional device operation is not implied. ? electrical characteristics (0 c Q t a Q 70 c, v cc =15v, r t =10k , c t =3.3nf, unless otherwise specified) parameter symbol test conditions min typ max unit reference section output voltage v ref t j =25 c,i out =1ma 4.9 5 5.1 v line regulation v ref 12 Q v in 25v 6 20 mv load regulation v ref 1 Q i out =20ma 6 25 mv temperature stability (n ote 1) 0.2 0.4 mv/ c total output variation line, load, temp(note 1) 4.82 5.18 v output noise voltage v osc 10hz Q f Q 10khz,t j =25 c (note 1) 50 v long term stability ta=25 c,1000hrs(note 1) 5 25 mv output short circuit i sc -30 -100 -180 ma oscillator section initial accuracy f t j =25 c 47 52 57 khz voltage stability f/ vcc 12 Q v cc Q 25v 0.2 1 % temperature stability tmin Q t a Q tmax(note 1) 5 % amplitude vosc vpin 4 peak to peak 1.7 v error amplifier section input voltage v i(ea) vpin 1=2.5v 2.42 2.50 2.58 v input bias current i i(bias) -0.3 -2 a avol 2 Q v out Q 4v 60 90 db unity gain bandwidth t j =25 c (note 1) 0.7 1 mhz psrr i2 Q v cc Q 25v 60 70 db output sink current i o(sink) vpin 2=2.7v,vpin 1=1.1v 2 6 ma output source current i o(source) vpin 2=2.3v,vpin 1=5v -0.5 -0.8 ma v out high v oh vpin 2=2.3v, r l =15k to gnd 5 6 v v out low v ol vpin 2=2.7v,vpin 1=1.1v 0.7 1.1 v
UC3842A/3843a linear integrated circuit unisonic technologies co., ltd 4 of 9 www.unisonic.com.tw qw-r103-002.f ? electrical characteristics(cont.) parameter symbol test conditions min typ max unit current sense section gain g v (note 2,3) 2.85 3 3.15 v/v maximum input signal v i(max) vpin 1=5v( note 2) 0.9 1 1.1 v psrr 12 Q v cc Q 25v 70 db input bias current i bias -2 -10 a delay to output vpin 3=0 to 2v 150 300 ns output section i o(sink) =20ma 0.1 0.4 v low v ol i o(sink) =200ma 1.5 2.2 v i o(source) =20ma 13 13.5 v output level high v oh i o(source) =200ma 12 13.5 v rise time t r t j =25 c,c l =1nf(note 1) 50 150 ns fall time t f t j =25 c,c l =1nf(note 1) 50 150 ns under-voltage lockout output section 3842a 14.5 16 17.5 v start threshold 3843a v th(st) 7.8 8.4 9 v 3842a 8.5 10 11.5 v min. operating voltage 3843a v opr(min) after turn on 7 7.6 8.2 v pwm section max d (max) 95 97 100 % duty cycle min d (min) 0 % total standby current start-up current i st 0.12 0.3 ma operating supply current i cc(opr) vpin 2=vpin 3=0v 11 17 ma v cc zener voltage v z i cc =25ma 34 v note:1.these parameters, although guarant eed ,are not 100% tested in production. 2. parameters measured at trip point of latch with vpin 2=0. 3. gain defined as: 4. adjust v cc above the start threshold before setting at 15v.
UC3842A/3843a linear integrated circuit unisonic technologies co., ltd 5 of 9 www.unisonic.com.tw qw-r103-002.f ? open-loop laboratory test fixture high peak current associated with capacity loads ne cessitate careful grounding techniques. timing and bypass capacitors should be connected close to pin 5 in single point gnd. the transistor and 5k potentio-meter are used to sample the oscillator waveform and apply an adjustable ramp to pin 3. ? under-voltage lockout during under-voltage lockout, the output driver is bi ased to a high impedance state. pin 6 should be shunt to gnd with a bleeder resistor to prevent activating the power switch with output leakage currents. ? error amplifier configuration 2 1 0.5ma 2.5v zf zi error amplifier can source or sink up to 0.5ma
UC3842A/3843a linear integrated circuit unisonic technologies co., ltd 6 of 9 www.unisonic.com.tw qw-r103-002.f ? current sense circuit 5 3 1 2r r1v c rs r is error amplifier current sense comparator peak current (is) determined by the formula: ismax=1.0v/rs. a small rc filter be required to suppress switch transients. ? slope compensation 0.1 f a fraction of the oscillator ramp c an be resistively summed with the current sense signal to provide slope compensation for converts requiring duty cycles over 50%.no te that capacitor c, forms a filter with r2 to suppress the leading edge switch spikes. ? oscillator section dead time vs. c t (r t >5k ) timing resistance vs. frequency td ( s) rt (k )
UC3842A/3843a linear integrated circuit unisonic technologies co., ltd 7 of 9 www.unisonic.com.tw qw-r103-002.f ? shutdown techniques 8 3 330 500 1k 1 shutdown to current sense resistor shutdown shutdown utc UC3842A can be accomplished by two methods; either raise pin 3 above 1v or pull pin 1 below a voltage two diode drops above ground. either method caused the output of pw m comparator to be high(refer to block diagram).the pwm latch is reset dominant so that the output will remain low until the next clock cycle after the shutdown condition at pins 1 and/or 3 is removed . in one example, an externally latched shut ?down may be accomplished by adding an scr which be reset by cycling v cc below the lower uvlo threshold. at this point the reference turns off allowing the scr to reset .
UC3842A/3843a linear integrated circuit unisonic technologies co., ltd 8 of 9 www.unisonic.com.tw qw-r103-002.f ? typical characteristics output saturation characteristics error amplifier open-loop frequency response saturation voltage (v) voltage gain (db) phase (degree) -50 -25 0 25 50 75 100 125 150 4.96 4.97 4.98 4.99 5.00 5.01 5.02 temperature ( ) vcc=15v i out =1ma -50 -25 0 25 50 75 100 125 150 250 300 350 400 450 500 550 temperature ( ) vcc=9v v ref temperature drift istart temperature drift
UC3842A/3843a linear integrated circuit unisonic technologies co., ltd 9 of 9 www.unisonic.com.tw qw-r103-002.f utc assumes no responsibility for equipment failures that result from using products at values that exceed, even momentarily, rated values (such as maximum ratings, operating condition ranges, or other parameters) listed in products specifications of any and all utc products described or contained herein. utc products are not designed for use in life support appliances, devices or systems where malfunction of these products can be reasonably expected to result in personal injury. reproduction in whole or in part is prohibited without the prior written consent of the copyright owner. the information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and may be changed without notice.
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