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unisonic technologies co., ltd uc3842b/3843b linear integrated circuit www.unisonic.com.tw 1 of 11 copyright ? 2008 unisonic technologies co., ltd qw-r103-012.d high performance current mode controllers ? description the utc uc3842b/3843b are specifically designed for off-line and dc-to-dc converter applicat ions offering the designer a cost-effective solution with mi nimal external components. the uc3842b has uvlo thresholds 16v (on) and 10v(off), ideally suited for off-line converters. the uc3843b is tailored for lower voltage applications having uvlo thresholds of 8.4v(on) and 7.6v(off). ? features * trimmed oscillator for precise frequency control * oscillator frequency guaranteed at 250khz * current mode operation to 500khz * automatic feed forward compensation * latching pwm for cycle-by-cycle current limiting * internally trimmed reference with undervoltage lockout * high current totem pole output * undervoltage lockout with hysteresis * low startup and operating current lead-free: uc3842bl uc3843bl halogen-free: uc3842bp uc3843bp ? ordering information ordering number normal lead free halogen free package packing uc3842b-d08-t UC3842BL-D08-T uc3842bp-d08-t dip-8 tube uc3842b-s08-r uc3842bl-s08-r uc3842bp-s08-r sop-8 tape reel uc3843b-d08-t uc3843bl-d08-t uc3843bp-d08-t dip-8 tube uc3843b-s08-r uc3843bl-s08-r uc3843bp-s08-r sop-8 tape reel
uc3842b/3843b linear integrated circuit unisonic technologies co., ltd 2 of 11 www.unisonic.com.tw qw-r103-012.d ? pin configuration 1 2 3 4 8 7 6 5 v cc output cs r t c t v ref comp v fb gnd ? pin descriptions pin no. pin name i/o description 1 comp o error amp output to provide loop compensation maintaing v fb at 2.5v 2 v fb i error amp inverting input, the non-invert ing input of error amp is 2.5v band gap reference 3 cs i current sense input to pw m control gate drive of output 4 r t c t i to set oscillator frequency and maximum output duty cycle 5 gnd power ground 6 output o to direct drive power mosfet 7 v cc power supply 8 v ref o 5v regulated output provides charging current for c t through r t
uc3842b/3843b linear integrated circuit unisonic technologies co., ltd 3 of 11 www.unisonic.com.tw qw-r103-012.d ? block diagram
uc3842b/3843b linear integrated circuit unisonic technologies co., ltd 4 of 11 www.unisonic.com.tw qw-r103-012.d ? absolute maximum ratings (ta=25 c) parameter symbol ratings unit total power supply and zener current (i cc + iz) 30 ma output current, source or sink (note1) io 1.0 a output energy (capacitive load per cycle) w 5.0 j current sense and voltage feedback inputs v in -0.3 ~ +5.5 v error amp. output sink current i o(sink) 10 ma dip-8 1250 mw power dissipation sop-8 p d 702 mw operating junction temperature t j +150 c operating temperature t opr 0 ~ +70 c storage temperature range t stg -65 ~ +150 c note absolute maximum ratings are those values beyond which the device could be permanently damaged. absolute maximum ratings are stress ratings only and functional device oper ation is not implied. ? thermal data parameter symbol ratings unit dip-8 100 c/w thermal resistance junction to ambient sop-8 ja 178 c/w ? electrical characteristics (0 c t a 70 c, v cc =15v [note 2], r t =10k, c t =3.3nf, unless otherwise specified) parameter symbol test conditions min typ max unit reference section output voltage v ref io=1.0ma, t j =25 c 4.9 5.0 5.1 v line regulation v line v cc =12v ~ 25v 2.0 20 mv load regulation v load io=1.0ma ~ 20ma 3.0 25 mv temperature stability t s 0.2 mv/ c total output variation v ref line, load, temper ature 4.82 5.18 v output noise voltage en f=10khz ~ 10hz, t j =25 c 50 uv long term stability s t a =125 c,1000hrs 5 mv output short circuit current i sc -30 -85 -180 ma oscillator section frequency f t j =25 c t a =0 c ~ 70 c t j =25 c (r t =6.2k,c t =1.0nf) 49 48 225 52 250 55 56 275 khz frequency change with voltage f osc / v 12 v cc 25v 0.2 1.0 % frequency change with temperature f osc / t 0 c t a 70 c 0.5 % oscillator voltage swing(peak to peak) v osc 1.6 v discharge current idischg t j =25 c 0 c t a 70 c 7.8 7.6 8.3 8.8 8.8 ma error amplifier section voltage feedback input v fb vo=2.5v 2.42 2.50 2.58 v input bias current i i(bias) v fb =5.0v -0.1 -2.0 a open loop voltage gain g vo 2 vo 4v 65 90 db unity gain bandwidth gb w t j =25 c 0.7 1.0 mhz power supply rejection ratio psrr i2v vcc 25v 60 70 db output sink current i sink vo=1.1v,v fb =2.7v 2.0 12 ma output source current i source vo=5.0v,v fb =2.3v -0.5 -1.0 ma output voltage swing high state v oh v fb =2.3v, r l =15k to gnd 5.0 6.2 v
uc3842b/3843b linear integrated circuit unisonic technologies co., ltd 5 of 11 www.unisonic.com.tw qw-r103-012.d ? electrical characteristics (cont.) parameter symbol test conditions min typ max unit output voltage swing low state v ol v fb =2.7v, r l =15k to v ref 0.8 1.1 v current sense section current sense input voltage gain g v (note 3,4) 2. 85 3.0 3.15 v/v maximum current sense input threshold v i(thr) (note 3) 0.9 1.0 1.1 v power supply rejection ratio psrr 12 vcc 25v (note 3) 70 db input bias current i i(bias) -2 -10 a propagation delay t d(in/out) current sense input to output 150 300 ns output section i sink =20ma 0.1 0.4 v output low voltage v ol i sink =200ma 1.6 2.2 v i source =20ma 13 13.5 v output high voltage v oh i source =200ma 12 13.4 v output voltage with uvlo activated v ol (uvlo) v cc =6.0v,i sink =1.0ma 0.1 1.1 v output voltage rise time t r t j =25 c,c l =1nf 50 150 ns output voltage fall time t f t j =25 c,c l =1nf 50 150 ns under-voltage lockout section utc uc3842b 14.5 16 17.5 v startup threshold v thr utc uc3843b 7.8 8.4 9 v utc uc3842b 8.5 10 11.5 v min. operating voltage after turn-on(vcc) v cc(min) utc uc3843b 7.0 7.6 8.2 v pwm section max 94 96 % duty cycle min dc 0 % total device power startup supply current i cc +i c v cc =6.5v for uc3843b v cc =14v for uc3842b 0.3 0.5 ma power operating supply current i cc +i c note2 12 17 ma power supply zener voltage v z i cc =25ma 30 36 v 1. 2. 3. maximum package power dissipation limits must be observed. adject v cc above the startup threshold before setting to 15v. this parameter is measured at the latch trip point with v fb =0v. v output compensation note: 4. comparator gain is defined as : g v v current sense input
uc3842b/3843b linear integrated circuit unisonic technologies co., ltd 6 of 11 www.unisonic.com.tw qw-r103-012.d ? typical application circuit open loop test circuit all of the parameters are not all tested in production, although been guaranteed. the timing and bypass capacitors must be connected to pin 5 in a single point ground very closely. to sample the oscillator waveform, the transistor and 5k ? potentiometer are used, and also can apply an adjustable ramp to i sense pin. 1 2 3 4 8 7 6 5 utc uc3842b/3843b comp v fb i sense r t /c t gnd output v c v ref a e/a adjust 1k 4.7k i sense adjust 5k 4.7k 2n 2222 r t 100k c t 0.1 0.1 output 1k/1w v1 v ref under voltage lockout under-voltage lock-out: the output driver is biased to a high impedance state. to prevent activating the power switch with output leakage current, pin 6 should be shunted to ground with a bleeder resistor. error amp configuration
uc3842b/3843b linear integrated circuit unisonic technologies co., ltd 7 of 11 www.unisonic.com.tw qw-r103-012.d ? application information(cont.) current sense circuit peak current (i s ) is equaled: i s(max) =1.0v/r s there should be a small rc filter to suppress switch transients. oscillator waveforms a nd maximum duty cycle 8 5 4 v ref r t /r c gnd c t r t interinal clock interinal clock v 4 v 4 large r t small c t small c t large r t c t (oscillator timing capacitor) can be charged by v ref through r t and discharged by an internal current source. at discharge time, the internal clock signal blanks the output to the low. both oscillator frequency and maximum duty cycle can be determined by selection of r t and c t . all charge and discharge times can be calculated by the next formulas: t c =0.55 r t c t t d =r t c t i n ? ? ? ? ? ? ? ? ? ? 4 0.0063r 2.7 0.0063r t t
uc3842b/3843b linear integrated circuit unisonic technologies co., ltd 8 of 11 www.unisonic.com.tw qw-r103-012.d ? application information(cont.) shutdown techniques the utc uc3842b?s shutdown can be accomplished by two ways: raise pin 3 above 1v; or pull pin 1 below a voltage two diode drops above ground. either method can cause the pwm comparator?s output to be high. because the pwm latch is reset dominant, the output will remain low until the next clock cycle after the shutdown condition at pins 1 and/or 3 is removed. slope compensation
uc3842b/3843b linear integrated circuit unisonic technologies co., ltd 9 of 11 www.unisonic.com.tw qw-r103-012.d ? typical characteristics discharge current, idischg (ma) timing resistor, r t (k ) c t =2 0 0 p f c t =1.0nf c t =5 .0nf c t =1 0 n f percent output deadtime, %dt. maximum output duty cycle, dmax (%) 20mv/div
uc3842b/3843b linear integrated circuit unisonic technologies co., ltd 10 of 11 www.unisonic.com.tw qw-r103-012.d ? typical characteristics(cont.)
uc3842b/3843b linear integrated circuit unisonic technologies co., ltd 11 of 11 www.unisonic.com.tw qw-r103-012.d ? typical characteristics(cont.) supply current, icc (ma) uc3842b uc3843b 100ma/div 20v/div supply current, icc output voltage, vo output saturation voltage, vsat (v) 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 specificatio ns 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 expect ed to result in personal injury. reproduction in whole or in part is prohibited without the prior writ ten 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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