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UC3843 fixed frequency current mode pwm controller 1 rev 1.0 jun. 2008 description features application ordering information temperature range package orderable device package qty sop8l pb-free UC3843d 75units/tube dip8l pin configuration UC3843p 50units/tube UC3843 is a fixed frequency current-mode pwm controller. it is specially designed for off line and dc-to-dc converter applications with minimal external component. this integrated circuit features a trimmed oscillator for precise duty cycle control, a temperature compensated reference, a high gain error amplifier, a current sensing comparator, and a high current totem pole output ideally suited for driving a power mosfet. the device is protective features consisting of input and reference under-voltage lockouts each with hysteresis, cycle-by-cycle current limiting. 1 2 3 4 5 6 7 8 (top view) compensation voltage feedback current sense r t /c t v ref v cc output gnd wireless base station power telecom and datacom power industrial power systems pc power supplies automatic feed forward compensation high current totem pole output internally trimmed bandgap reference undervoltage lockout with hysteresis low start up current optimized for offline converter double pulse suppression current mode operation to 500khz 0c to +70c
UC3843 2 rev 1.0 jun. 2008 schematic diagram pin description no. name function description 1 compensation this pin is the error amplifier output and is made available for loop compensation. 2 voltage feedback this is the inverting input of the error amplifier. it is normally connected to the switching power supply output through a resistor divider. 3 current sense a voltage proportional to inductor current is connected to this input the pwm uses this information to terminate the output switch conduction. 4r t /c t the oscillator frequency and maximum output duty cycle are programmed by connecting resistor rt to v ref and capacitor c t to ground. operation to 500khz is possible. 5 gnd this pin is the combined control circuitry and power ground. 6 output this output directly drives the gate of a power mosfet. peakcurrents up to 1.0a are sourced and sunk by this pin. 7v cc this pin is the positive supply of the control ic. 8 v ref this is the reference output. it provides charging current for capacitor c t through resistor r t figure 1. simplified block diagram + - v ref 8(14) r t c t 4(7) voltage feedback input 2(3) output compensation 1(1) v cc 7(12) v c 7(11) output 6(10) power ground 5(8) current sense input 3(5) gnd 5(9) error amplifier oscillator latching pwm v ref undervoltage lockout 5.0v reference v cc undervoltage lockout pin numbers in parenthesis are for the d suffix soic-14 package. r r
UC3843 3 rev 1.0 jun. 2008 absolute maximum ratings symbol value unit total power supply and zener current i cc + i z 30 dc supply voltage v cc 30 v output current i o 1.0 a output energy (capacitive load per cycle) w 5.0 j error amp output sink current i oe 10 ma current sense and voltage feedback inputs v in -0.3 to 5.5 v maximum power dissipation @t a =25 c p d 0.862 w thermal resistance, junction-to-air r bia 145 c/w maximum operating junction temperature t j +150 c storage temperature range t stg -65 to +150 parameter symbol min max unit dc supply voltage v cc 12 25 v ma c parameter operating temperature t a 070 c electrical characteristics (vcc = 15v unless otherwise noted) parameter symbol test conditions min max unit 4.9 5.1 reference out v ref 4.865 5.135 v line regulation reg line 20 mv load regulation reg load 25 mv total output variation over line, load, temperature (note1) v final 4.82 5.18 v output short circuit current i sc -30 -180 ma recommended operation conditions i o = 1.0ma, v cc = 15v, t a = 2510c io = 1.0ma, v cc = 15v, t a = t low to t high v cc = 12v to 25v, t a = t low to t high i o = 1.0 to 20ma, t a = t low to t high v cc = 12v, i o = 1.0ma, t a = t low to t high v cc = 25v, i o = 20ma, t a = t low to t high v cc =15v reference section
UC3843 4 rev 1.0 jun. 2008 v cc = 15v, t j = 25 c r t =10k ? , c t = 3.3nf 47 57 frequency f osc v cc = 15v , t a = t low to t high , r t = 10k ? c t = 3.3nf 46 60 khz frequency change with voltage f osc /v 1.0 % t j = 25 c 7.5 9.3 discharge current i disch v osc = 2.0v v cc = 15v t a = t low to t high 7.2 9.5 ma error amplifier section voltage feedback input v fb v o = 2.5v ,v cc = 15v, t a = t low to t high 2.42 2.58 v input bias current i ib v fb = 2.7v,v cc = 15v, ta = t low to t high -2.0 a open loop voltage gain a vol v o = 2.0v to 4.0v, v cc = 15v, t a = t low to t high 65 db unity gain bandwidth bw v cc = 15v, t a = t low to t high 0.7 mhz power supply rejection ratio psrr v cc = 12v to 25v, t a = t low to t high 60 db sink i sink v o = 1.1v, v fb = 2.7v, v cc = 15v, t a = t low to t high 2.0 output current source i source v o = 5.0v, v fb = 2.3v, v cc = 15v, t a = t low to t high -0.5 ma high state v oh 5.0 output voltage swing low state v ol v fb = 2.7v, v cc = 15v r l(5.0) = 15k, t a = t low to t high 1.1 v oscillator section v fb = 2.7v, v cc = 1 5v r l(gnd) = 15k, t a = t low to t high electrical characteristics parameter symbol test conditions min max unit v cc = 12v to 25v, t a = t low to t high, r t = 10k, c t =3.3nf
UC3843 5 rev 1.0 jun. 2008 output section i sink = 20ma, v cc = 15v 0.4 low state v ol i sink = 200ma, v cc = 15v 2.2 13 output voltage high state v oh 12 v output voltage with uvlo activated v ol(uvlo) v cc = 6v, i sink = 1.0ma, t a = t low to t high 1.1 v t r c l = 1.0nf,v cc = 15v, t a = t low to t high 150 ns output voltage fall time t f 150 ns under voltage lockout section startup threshold v th 7.8 7.9 v minimum operating voltage after turn-on v cc(min) 7.0 8.2 v pwm section duty cycle dc v cc = 15v, t a = t low to t high , r t = 10k, c t = 3.3nf 0 94 % total device startup: v cc = 14v 1.0 power supply current i cc operating: v cc = 15v 17 ma power supply zener voltage v z i cc = 25ma, v cc = 0 to 40v 30 40 v note 1 : v final = v ref25 (reg line +reg load )/1000iv ref70 (v ref0 )-v ref25 i v ref25 = v ref @t a =25c; v ref70 =v ref @t a =70c;v ref0 =v ref @t a =0c. note 2 : t low = 0c,t high =+70c i sink = 20ma, v cc = 15v i sink = 200ma, v cc = 15v v cc = 0v to 25v, t a = t low to t high output voltage rise time current sense section current sense input voltage gain a v v fb = 0v, v cc = 15v, t a = t low to t high 2.85 3.15 maximum current sense input threshold v th 0.9 1.1 v input bias current i ib -10 a propagation delay (current sense input to output) t plh 300 ns v fb = 0v,v cc = 15v, t a = t low to t high v cc = 15v, t a = t low to t high v cc = 15v, t a = t low to t high electrical characteristics(continue) parameter symbol test conditions min max unit c l = 1.0nf, v cc = 15v, t a = t low to t high v cc = 0v to 25v, t a = t low to t high
UC3843 6 rev 1.0 jun. 2008 figure 2. timing resistor versus oscillator frequency figure 3. output deadtime versus oscillator frequency figure 4. oscillator discharge current versus temperature figure 5. maximum output duty cycle versus timing resistor figure 6. error amp small signal transient response figure 7. error amp large signal transient response v cc = 15v v osc = 20v 2.55v 2.5v 2.45v 2.5v 3.0v 2.0v 100 50 20 10 5.0 2.0 1.0 9.0 8.5 8.0 7.5 7.0 100 90 80 70 60 50 40 typical performance characteristics f osc ,oscillator frequency (hz) v cc = 15v t a = 25c 80 50 20 8.0 5.0 2.0 0.8 r t , timing resistor (k) 10k 20k 50k 100k 200k 500k 1.0m % dt,percent outputdeadrme 10k 20k 50k 100k 200k 500k 1.0m v cc = 15v t a = 25c f osc ,oscillator frequency (hz) i dischg , discharge current (ma) -55 -25 0 25 50 75 100 125 t a , ambient temperature (c) d max , maximum output duty cycle (%) 800 1.0k 2.0k 3.0k 4.0k 6.0k 8.0k i dischg = 9.5 ma i dischg = 7.2 ma v cc = 15 v c t = 3.3 nf t a = 25c rt, timing resistor () v cc = 15 v a v = -1.0 t a = 25c 20 mv/div 0.5 s/div v cc = 15 v a v = -1.0 t a = 25c 20 mv/div 0.1 s/div
UC3843 7 rev 1.0 jun. 2008 typical performance characteristics(continue) figure 8. error amp open loop gain and phase versus frequency figure 9. current sense input threshold versus error amp output voltage figure 10. reference voltage change versus source current figure 11. reference short circuit current versus temperature figure 12. reference load regulation figure 13. reference line regulation ?vo,output voltage change(2.0mv/div) 2.0 ms/div 2.0 ms/div v cc =12v to 25v i ref , reference source current (ma) v cc =15v t a =-55c t a =125c t a , ambient temperature (c) i sc ,reference short circuit current(ma) 0 110 90 70 50 t a =25c gain phase 0 30 60 90 120 150 180 0 20 40 60 80 100 0 0.2 0.4 0.6 0.8 1.0 1.2 v cc = 15v t a = 25c t a = -55c -4.0 -8.0 -12 -16 -20 -24 t a = 25c ?vo,output voltage change(2.0mv/div) -20 10 100 1.0k 10k 100k 1.0m 10m a vol , open loop voltage gain (db) f, frequency (hz) v cc = 15 v v o = 2.0 v to 4.0 v r l = 100 k t a = 25c f, excess phase (degrees) vth, current sense input threshold (v) t a = 125c 0 2.0 4.0 6.0 8.0 v o , error amp output voltage (v) ?v ref , reference voltage change (mv) 0 20 40 60 80 100 120 v cc = 15 v r l 0.1 -55 -25 0 25 50 75 100 125 v cc = 15 v i o = 1.0 ma to 20 ma t a = 25c
UC3843 8 rev 1.0 jun. 2008 typical performance characteristics(continued) figure 14. output saturation voltage versus load current figure 15. output waveform figure 17. supply current versus supply voltage 50 ns/div c l = 1.0nf 100 ns/div v cc = 15v c l = 15pf i cc ,supply current,v o ,output voltage 800 600 400 200 0 i o , output load current (ma) v sat ,output saturation voltage(v) v cc ta = 25c t a =-55c gnd t a = 25c source saturation (load to ground) v cc = 15v 80 s pulsed load 120 hz rate v cc , supply voltage(v) i cc ,supply current(ma) r t = 10k c t = 3.3nf v fb = 0v i sense = 0v 90% 10% 0 1.0 2.0 3.0 0 25 20 15 10 5 0 sink saturation (load to v cc ) t a =-55c -2.0 -1.0 t a = 25c v cc = 15v t a = 25c t a = 25c 100 ma/div 20 v/div ucx842a ucx843a figure 16. output cross conduction
UC3843 9 rev 1.0 jun. 2008 typical application r1 5 1w 117 vac varo vm 68 c1 250 f 250v r2 56k 2w r4 4.7k r3 20k r5 150 k c14 100 pf c5 0.01 f r6 10 k c6 0.0022 f uc3844 c2 100 f 25v c3 22 f r9 68 3w c4 47 f 25v nc d2 1n3612 d3 1n3612 usd1120 c7 470pf 1k r8 r7 22 r12 4.7k 2w c9 3300pf 600v d4 1n3613 n p t1 d6 u9d946 l1 n5 c10 4700 f 10v c11 4700 f 10v r13 20k q1 ufn833 r10 0.55 1w n12 n12 d7 uf81002 d8 ues1002 c12 2200 f 16v c13 2200 f 16v c8 680pf 600v d8 1n3613 r11 2.7k 2w +6v com +12v 12v com ?12v 7 2 1 8 4 5 3 6
UC3843 10 rev 1.0 jun. 2008 physical dimensions a a1 a2 a3 b b1 c c1 c2 4.95 5.15 0.37 0.47 1.27(typ) 0.41(typ) 5.80 6.20 3.80 4.00 0.55 0.65 c4 d d1 r1 r2 0.05 0.20 1.05(typ) 0.20(typ) 0.07(typ) 13 (typ) 4 (typ) 12 (typ) 1 2 3 4 b2 0.65 0.55 1.30 1.50 5.0(typ) c3 17 (typ) a2 a3 a a1 b2 c 4 d1 r2 r1 c1 c2 c c3 d 0.40 0.60 0.07(typ) b sop8l physical dimensions symbol dimension(mm) min max symbol dimension(mm) max min b1 1 2 3 4
UC3843 11 rev 1.0 jun. 2008 symbol min max a a1 a2 a3 a4 a5 b c 1.524(typ) 0.39 0.53 2.54(typ) 0.66(typ) 0.99(typ) 6.3 6.5 symbol min max c2 c4 d d1 d2 8.20 0.20 7.62 5 (typ) 8.80 0.35 7.87 dimension(mm) dimension(mm) 1 9.30 9.50 c1 7.20 (typ) 3.30 3.50 2 3 c3 0.5 (typ) 3.3 (typ) 8 (typ) 8 (typ) 1.57(typ) c1 c2 c3 c4 a1 a2 a3 a4 a5 d2 d1 a b c d dip8l 1 2 3

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