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unisonic technologies co., ltd uc3848 linear integrated circuit www.unisonic.com.tw 1 of 12 copyright ? 2008 unisonic technologies co., ltd qw-r103-033.c high performance current mode controllers ? description the utc uc3848 is designed to provide several special enhancements to satisfy the needs: power-saving mode for low standby power, over current pr otection (ocp), over voltage protection (ovp), over load protec tion (olp), over temperature protection (otp) etc protection feat ures. ic will be shutdown when either protection arise and can aut o-restart. uvlo featuring typical start-up current 20a, and v cc(on) 12.6v, v cc(off) 8.1 7 . lower typical operation current icc 3.7m a at inactive output. the output stage, suitable for driving n-chan nel mosfets, can operate to duty cycles approach 70%. the uc3848 are fully pin-to-pin compatible with uc3842 except v ref -pin and nc-pin. v ref -pin?s application as application circuits. pin fb with an 4k ? pull up resistor to internal reference voltage. the uc3848 also have soft-start function avoiding overshoot, and controlled driver output rise edge time t r for low emi. ? features * low startup and operation current * 68khz switching frequency * max duty cycle 70% * power-saving mode for low power * under voltage lockout with hysteresis * over temperature protection * overload protection * over voltage protection * leading edge blanking * soft start *pb-free plating product number: uc3848l ? ordering information ordering number normal lead free plating package packing uc3848-d08-t uc3848l-d08-t dip-8 tube uc3848-s08-r uc3848l-s08-r sop-8 tape reel uc3848-s08-t uc3848l-s08-t sop-8 tube
uc3848 linear integrated circuit unisonic technologies co., ltd 2 of 12 www.unisonic.com.tw qw-r103-033,c ? pin configuration out gnd v cc v ref nc cs fb ss 1 2 3 4 8 7 6 5 ? pin description pin no. symbol function 1 ss soft-start 2 fb feedback 3 cs controller current sense input 4 nc 5 out ground 6 gnd output to the gate of external power mos 7 v cc supply voltage 8 v ref inter 6.3v reference voltage, conn ected with the filter capacitor
uc3848 linear integrated circuit unisonic technologies co., ltd 3 of 12 www.unisonic.com.tw qw-r103-033,c ? block diagram v cc ss fb gnd out latch oscillator s rq q driver current limiting pwm comp soft start power-saving unit ovp olp otp uvlo reference voltage cs v ref nc 8 7 1 2 6 3 5 4 leb explain:olp(over load protection) ovp(over voltage protection) otp(over temperature protection) uvlo(under voltage latch-out leb(led edge blanking) ss(soft start)
uc3848 linear integrated circuit unisonic technologies co., ltd 4 of 12 www.unisonic.com.tw qw-r103-033,c ? absolute maximum ratings (ta " 25c, v cc =15v, unless otherwise specified) parameter symbol ratings unit supply voltage v cc 26 v input voltage to fb pin v fb -0.3 ~ 6.2 v input voltage to cs pin v cs -0.3 ~ 2.8 v junction temperature t j +150 c operating temperature t opr -40 ~ +125 c storage temperature t stg -50 ~ +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. ? recommended operating conditions parameter symbol ratings unit supply voltage v cc 8.2 ~ 21 v ? electrical characteristics (ta " 25c, v cc =15v, unless otherwise specified) parameter symbol test conditions min typ max unit supply section start up current i str v cc =12.5v 27 45 a off i off v ss = 0, i fb = 0 3.7 5.5 ma supply current with switch on i on v ss = 5v, i fb = 0 4.0 6.0 ma under-voltage lockout section start threshold voltage v thd(on) 11.8 12.6 13.4 v min. operating voltage v cc(min) 7.6 8.1 8.6 v hysteresis v cc(hy) 4.5 v internal voltage reference reference voltage v ref measured at pin v ref 6.1 6.3 6.6 v control section normal v fb = 4v 61 68 75 khz switch frequency power-saving f (sw) v fb = 1v 17 20 24 khz max d max 65 70 75 % duty cycle min d min v fb < 0.5v 0 % min v min 0.5 v v fb operating level max v max 4.4 v feedback resistor r fb 2.6 3.8 5.0 k ? c ss =0.05uf 6 ms c ss =0.1uf 12 ms soft-start time t ss c ss =1uf 120 ms protection section ovp threshold v (ovp) v ss < 3.5v, v fb > 5v 15.2 16 16.8 v olp threshold v fb(olp) v ss > 5.4v 4.4 4.6 4.9 v otp threshold t (thr) 120 135 150 c ovp disable threshold v ss(deact) v fb > 5v, v cc > 17v 3.7 3.9 4.2 v olp enable threshold v ss(act) v fb > 5v 4.9 5.1 5.4 v spike blanking time t sb 7.2 s current limiting section leb t leb 220 ns driver output section output voltage low state v ol i source = 200 ma 2.5 v output voltage high state v oh i sink = 200 ma 12.2 v output voltage rise time t r c l = 1.0 nf 300 400 ns output voltage fall time t f c l = 1.0 nf 50 90 ns
uc3848 linear integrated circuit unisonic technologies co., ltd 5 of 12 www.unisonic.com.tw qw-r103-033,c ? functional description the internal reference voltages and bias circuit work at v cc >12.6v, and shutdown at v cc < 8.1v. (1) soft-start when every ic power on, driver output duty cycle will be decided by voltage v ss on soft-start capacitor and v cs on current sense resistor at beginning. after v ss reach 5.1v, the whole soft-sta rt phase end, and driver duty cycle depend on v fb and v cs . the relation among v ss , v fb and v out as followed fig.3, here soft-start phase t soft-start should more than v out start-up phase t start-up , otherwise, ic will enter false olp protection state. because after the soft-start phase end, if v out remain in lower voltage, v fb more than 4.6v, then ic enter false olp state. furthermore, soft-start phase should end before v cc reach v cc(min) during v cc power on. otherwise, if soft-start phase remain not end before v cc reach v cc(min) during v cc power on, ic will enter auto -restart phase and not set up v out . finally soft-start also set ovp active phase. ovp active phase between v ss =0 and v ss =3.8v, ovp will not be sensed after v ss reach 3.8v.the soft-start phase t ss 6 ms (c ss =0.05uf) t ss = 12 ms (c ss =0.1uf) 120 ms (c ss =1uf) fig.3 soft-start phase
uc3848 linear integrated circuit unisonic technologies co., ltd 6 of 12 www.unisonic.com.tw qw-r103-033,c ? functional description(cont.) (2) switch frequency set the maximum switch frequency is 68khz. the switch frequency is also modulated by output power p out during ic operating. lower switch frequency at lower load can impr ove ic?s standby efficiency. switch frequency is decreased minimum at no load, then the uc3848 will operate at power-saving mode for lower standby power. the relation curve between f sw and p out as followed fig.4. fig.4 the relation curve between f sw and output power p out
uc3848 linear integrated circuit unisonic technologies co., ltd 7 of 12 www.unisonic.com.tw qw-r103-033,c ? functional description(cont.) (3) protection section uc3848 takes on more protection functions such as olp, o vp and otp etc. in case of those failure modes for continual 7.2 s (blanking time), the driver is shut down . at the same time, ic enters auto-restart, v cc power on and driver is reset after v cc power on again. olp after soft-start phase end (v ss >5.1v), ic will shutdown driver if over load state occurs (corresponding to v fb >4.6v) for continual 7.2 s. olp function will not inactive during soft-start phase. olp case as followed fig.6 . the test circuit as followed fig.8. fig.6 olp case fig.7 ovp case ovp power supply v cc ?s ovp function are enabled only when v ss <3.9v & v fb >4.6v during soft-start phase. during above condition, driver will be shutdo wn if over voltage state occurs (v cc >16v) for continual 7.2 s. ovp function will not inactive after soft-start phase. olp case as followed fig.7 . the test circuit as followed fig.9. otp otp will shut down driver when junction temperature t j of internal circuits is more than threshold 135c for continual 7.2 s.
uc3848 linear integrated circuit unisonic technologies co., ltd 8 of 12 www.unisonic.com.tw qw-r103-033,c ? functional description(cont.) c4 2 1 3 4 7 8 6 5 c3 c13 utc uc3848 r17 ic3 v cc 15v 5.5v driver c4 2 1 3 4 7 8 6 5 c3 c13 utc uc3848 r17 ic3 vcc 3.5v fig.8 olp test circuit fig.9 ovp test circuit v fb 7.2us 4.6v v fb driver 7.2us v cc 16v v fb (4) driver output section rise edge time of driver output is about 200ns for avoiding low emi. when driver output v ol(max) is less than 2.5v with 200ma source current, and v oh(min) is more than 12.2v with 200ma sink current. (5) external power switch mos transistor because uc3848 driver output voltage low level thre shold is about 2.5v, user may apply power mos transistors with bigger threshold. 4n60 is recommended normally.
uc3848 linear integrated circuit unisonic technologies co., ltd 9 of 12 www.unisonic.com.tw qw-r103-033,c ? typical application circuit 5v 3a + gnd ic2 cy1 c2 ic1 rf r2 cd1 rd1 d1 c5 + r5 r4 r3 zd1 r12 l3 tr1 d3 c8 c12 r10 d2 r8 q1 r6 r c4 r17 + c3 c15 r11 c14 ic3 utc uc3848 4 3 2 1 5 6 7 8 th1 cx1 ac in f1 bd1 + c9 fig.12 uc3848 typical application circuit table1 components reference descrip tion for uc3848 application circuit c12 cc 10nf/1000v d3 diode uf1007 r r 470k ? 1/8w c14 cc 100nf/50v ic1 ic pc817 th1 sck-103 c2 cc 33nf/50v ic2 ic tl431clp bd1 r kbp-208 cx1 104/275v ic3 ic uc3848 rd1 r 10 ? 1/8w c5 ec 1000uf/15v l3 l 1.2uh r12 r 3.3k ? 1/8w c4 cc 22uf/50v q1 mos 4n60 tr1 optional c8 ec 68uf/400v rf r 4.7k ? 1/8w c9 ec 1000uf/16v r17 r 1.2 ? /1w 1/8w c15 cc 0.1 f/50v cd1 cc 1nf/1kv r2 r 680 ? 1/8w cy1 cc 4.7nf/250v r3 r adj 1/8w d1 diode c63-004 r4 r 5.6k ? 1/8w d2 diode 1n4148 r5 r 5.6k ? 1/8w note c5 and c9 are lower esr capacitors.
uc3848 linear integrated circuit unisonic technologies co., ltd 10 of 12 www.unisonic.com.tw qw-r103-033,c ? typical characteristics 100 0 125 200 efficiency vs. in put voltage at nominal load 20 300 150 250 10 30 40 60 50 70 80 100 90 efficiency (%) input votage (v dc ) 0 50 20 8 efficiency vs. output power 55 16 12 60 65 70 75 80 efficiency (%) output power (w) 18 614 10 4 2 efficiency (vdcin = 120v) efficiency (vdcin = 350v) frequency (khz) input power (w) output voltage (v dc ) output voltage(v dc )
uc3848 linear integrated circuit unisonic technologies co., ltd 11 of 12 www.unisonic.com.tw qw-r103-033,c ? typical characteristics(cont.) 120mv 3.86v 1.64khz 850hz ch1 max 6.00v ch1 min 460mv ch1 frequency 785.5hz m 400 0 s a ch1 ? 3.18v 1.00v ch1 60.0mv 3.30v 3.29khz 1.70khz ch1 max 5.90v ch1 min 40.0mv ch1 frequency 1.906khz m 200 0 s a ch1 ? 2.68v 1.00v ch1 feedback voltage during loadjump from 10% up to 100% load (v dcin =120v) feedback voltage during loadjump from 10% up to 100% load (v dcin =350v) 12.3v 12.3v ch1 max 5.04v ch1 min 1.32v ch1 frequency -----hz m 10.0ms a ch1 ? 3.16v 2.00v ch1 startup with full load condition at v dcin =120v, vc4 and vout v c4 v out 5.00v ch2 12.3v 12.3v ch1 max 5.04v ch1 min -120mv ch1 frequency -----hz m 10.0ms a ch1 ? 3.16v 2.00v ch1 startup with full load condition at v dcin =350v, vc4 and vout v c4 v out 5.00v ch2
uc3848 linear integrated circuit unisonic technologies co., ltd 12 of 12 www.unisonic.com.tw qw-r103-033,c 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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