unisonic technologies co., ltd uc3844/45 linear integrated circuit www.unisonic.com.tw 1 of 7 copyright ? 2011 unisonic technologies co., ltd qw-r103-010.d high performance current mode pwm controllers ? description the utc uc3844/3845 are high performance fixed frequency current mode controllers that specifically designed for off-line and dc to dc converter applications with minimal external parts count. the differences between uc3844 and uc3845 are the maximum duty cycle ranges and under-voltage lockout thresholds. the uc3844 ideally suited to off-line applications with uvlo thresholds of 16v (on) and 10v (off) , and uc3845 has uvlo thresholds of 8.5v (on) and 7.6v (off) for lower voltage applications. ? features * operation output switchi ng frequency up to 500 khz * output deadtime adjustable from 50% to 70% * automatic feed forward compensation * latching pwm for cycle-by-cycle current limiting * high current totem pole output * internally trimmed reference with under voltage lockout * uvlo with hysteresis * low startup and operating current ? ordering information ordering number lead free halogen free package packing uc3844l-d08-t UC3844G-D08-T dip-8 tube uc3844l-s08-r uc3844g-s08-r sop-8 tape reel uc3844l-s08-t uc3844g-s08-t sop-8 tube uc3845l-d08-t uc3845g-d08-t dip-8 tube uc3845l-s08-r uc3845g-s08-r sop-8 tape reel uc3845l-s08-t uc3845g-s08-t sop-8 tube
uc3844/45 linear integrated circuit unisonic technologies co., ltd 2 of 7 www.unisonic.com.tw qw-r103-010.d ? pin configuration ? pin description pin no pin name function 1 compensation error amplifier output, this pin is made available for loop compensation. 2 v fb voltage feedback, the inverting input of the error amplifier. it is normally connected to the switching power supply output through a resistor divider. 3 i sense a voltage proportional to inductor current is connected to this input. the pwm uses this information to terminate the output switch conduction. 4 r t /c t the oscillator frequency and maximum output duty cycle are programmed by connecting resistor r t to vref and capacitor c t to ground. operation to 1 mhz is possible. 5 gnd power ground. 6 output this output directly drives the gate of a power mosfet. peak currents up to 1a are sourced and sunk by this pin. the output sw itches at one-half t he oscillator frequency. 7 v cc positive supply. 8 v ref reference output, provides charging current for capacitor c t though resistor r t .
uc3844/45 linear integrated circuit unisonic technologies co., ltd 3 of 7 www.unisonic.com.tw qw-r103-010.d ? block diagram
uc3844/45 linear integrated circuit unisonic technologies co., ltd 4 of 7 www.unisonic.com.tw qw-r103-010.d ? absolute maximum ratings (t a =25 c) parameter symbol ratings unit total power supply and zener current (i cc +iz) 30 ma output current, source or sink (note 2) i out 1.0 a output energy (capacitiv e load per cycle) w 5.0 j current sense and volt age feedback inputs v in -0.3 ~ +5.5 v error amp output sink current i sink 10 ma sop-8 862 mw power dissipation dip-8 p d 1250 mw junction temperature t j +150 c operation temperature t opr 0 ~ 70 c storage temperature t stg -65 ~ +150 c note:1. absolute maximum ratings are those values beyond which the device could be permanently damaged. note:1. absolute maximum ratings are stress ratings only and functional device operation is not implied. 2. maxmum package power di ssipation limits must be observed. ? thermal data parameter symbol ratings unit sop-8 145 c/w junction to ambient dip-8 ja 100 c/w ? electrical characteristics (t a =25 c, v cc =15v, r t =10k, c t =3.3nf, 0 c t a 70 c, unless otherwise specified) parameter symbol test conditions min typ max unit reference section reference output voltage v ref i out =1.0ma,t j =25 c 4.9 5.0 5.1 v line regulation v out v cc =12v ~ 25v 2.0 20 mv load regulation v out i out =1.0ma ~ 20ma 3.0 25 mv temperature stability t s 0.2 mv/ c total output variation over line, load, temperature v ref 4.82 5.18 v output noise voltage en f=10hz ~ khz, t j =25 c 50 v long term stability s t a =125 c for 1000 hours 5 mv output short circuit current i sc -30 -85 -180 ma oscillator section oscillator voltage swing v osc 1.6 v discharge current i dsg v osc =2.0v, t j =25 c 10.8 ma t j =25 c, 47 52 57 frequency f osc 0 c t a 70 c 46 60 khz frequency change with voltage f osc / v v cc =12v ~ 25v 0.2 1.0 % frequency change with temperature f osc / t 0 c t a 70 c 5.0 % error amplifier section voltage feedback input v fb v out =2.5v 2.42 2.50 2.58 v high v oh r l =15k to ground, v fb =2.3v 5.0 6.2 output voltage swing low v ol r l =15k to v ref , v fb =2.7v 0.8 1.1 v sink i sink v out =1.1v, v fb =2.7v 2.0 12 output current source i source v out =5.0v, v fb =2.3v -0.5 -1.0 ma input bias current i i(bias) v fb =2.7v -0.1 -2.0 a open loop voltage gain g vo v out =2.0v ~ 4.0v 65 90 db power supply rejection ratio psrr v cc =12v ~ 25v 60 70 db unity gain bandwidth gb w t j =25 c 0.7 1.0 mhz
uc3844/45 linear integrated circuit unisonic technologies co., ltd 5 of 7 www.unisonic.com.tw qw-r103-010.d ? electrical characteristics(cont.) parameter symbol test conditions min typ max unit current sense section current sense input voltage gain g v (note 2, 3) 2.85 3.0 3.15 v/v maximum current sense input threshold (note 2) v i(thr) 0.9 1.0 1.1 v input bias current i i(bias) -2.0 -10 a power supply rejection ratio psrr v cc =12v ~ 25v (note4) 70 db propagation delay t plh(in/out) 150 300 ns output section i sink =20ma 0.1 0.4 low v ol i sink =200ma 1.6 2.2 v i sink =20ma 13 13.5 output voltage high v oh i sink =200ma 12 13.4 v output voltage with u vlo activated v ol (u vlo )v cc =6.0v, i sink =1.0ma 0.1 1.1 v output voltage rise time t r c l =1.0nf,t j =25 c 50 150 ns output voltage fall time t f c l =1.0nf,t j =25 c 50 150 ns undervoltage lockout section uc3844 14.5 16.0 17.5 startup threshold uc3845 v thr 7.8 8.4 9.0 v uc3844 8.5 10.0 11.5 minimum operating voltage after turn-on uc3845 v cc(min) 7.0 7.6 8.2 v pwm section max dc max 47 48 50 % duty cycle min dc min 0 % total device power supply zener voltage v z i cc =25ma 30 36 - v uc3845 v cc =6.5v 0.5 1.0 power supply current (note 4) uc3844 i cc v cc =14v 12 17 ma note: 1. low duty cycle pulse techniques are used during te st to maintain junc tion temperature as close to ambient as possible. 2. this parameter is measured at the latch trip point with v fb =0v. 3. comparator gain is defined as: v output compensation a v = v current sense input 4. adjust v cc above the startup threshold before setting to 15v.
uc3844/45 linear integrated circuit unisonic technologies co., ltd 6 of 7 www.unisonic.com.tw qw-r103-010.d ? typical characteristics 100 50 10 5.0 1.0 10k 20k 50k 100k oscillator frequency, i osc (hz) timing resistor, r t (k ) 200k 500k 1.0m timing resistor vs. oscillator frequency 2.0 20 75 65 60 10k 20k 50k 100k percent output d eadtime, dt (%) 200k 500k 1.0m output deadtime vs. oscillator frequency 55 70 v cc = 15v t a = 25 1 0 0 p f 2 0 0 p f 5 0 0 p f 1 . 0 n f 2 . 0 n f 5 . 0 n f c t = 1 0 n f note: output switches at one-half the oscillator frequency 50 oscillator frequency, i osc (hz) 1.0nf 2.0nf 5.0nf c t = 10nf 100pf 200pf 500pf 100 80 40 20 -20 10 100 1.0k 10k frequency, f (hz) open loop voltage gain, g v (db) 100k 1.0m 10m error amp open loop gain phase vs. frequency 0 60 1.2 0.8 0.4 02.04.0 current sense input threshold, v in(thr) (v) 6.0 8.0 current sense input threshold vs. error amp output voltage 0.2 1.0 v cc = 15v v out = 2.0v ~ 4.0v r l = 100k t a = 25 phase gain 0 error amp output voltage, v out (v) excess phase degrees, 0 30 90 120 180 150 60 0.6 t a = 25 v cc = 15v t a = 125 t a = -55
uc3844/45 linear integrated circuit unisonic technologies co., ltd 7 of 7 www.unisonic.com.tw qw-r103-010.d ? typical characteristics(cont.) output saturation voltage, v o(sat) (v) supply current, i cc (ma) ucx844 ucx845 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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