unisonic technologies co., ltd uc2843b preliminary linear integrated circuit www.unisonic.com.tw 1 of 9 copyright ? 2009 unisonic technologies co., ltd qw-r103-048.a high-performance current-mode pwm controllers ? description the utc uc2843b provides off-line or dc-dc fixed-frequency current-mode control design with minimum external components. internally-implemented circuits include an under-voltage lockout (uvlo) and a precision reference with accuracy at the error amplifier input. the utc uc2843b also contain internal circuits which include a pulse width modulation (pwm) com parator providing current-limit control, logic ensuring latched o peration, and a totem-pole output stage designed to source or sink high-peak current. the output stage is low when it is in off- state condition and suitable for n-channel mosfets driving. the utc uc2843b also has following advantages: the start-up current lower than 0.5ma while the oscillator discharge current is specified to 8.3ma (typ.). in uv lo conditions, the output has a maximum saturation voltage of 1.2v when sinking 10ma @ v cc = 5v. the typical uvlo threshold of the utc uc2843b is 8.4v (on) and 7.6v (off) and can operate to duty cycles approximately 100%. ? features * current mode operation:500 khz * low start-up current value < 0.5ma * latching pwm for cycle-by-cycle current limiting * trimmed oscillator discharge current * automatic feed-forward compensation * internally trimmed reference with uvlo * high-current totem-pole output uvlo with hysteresis * double-pulse suppression * halogen free ? ordering information ordering number package packing UC2843BG-S08-R sop-8 tape reel
uc2843b preliminary linear integrated circuit unisonic technologies co., ltd 2 of 9 www.unisonic.com.tw qw-r103-048.a ? pin configuration v ref 8 7 6 5 1 2 3 4 r t /c t comp vfb i sense v cc output gnd ? pin description pin no. pin name description 1 comp this pin is the error amplifier output and is made available for loop compensation. 2 vfb this is 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 v ref and capacitor c t to ground. operation to 500 khz 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 . peak currents up to 1.0 a are sourced and sunk by this pin. 7 v cc this pin is the positive s upply of the control ic. 8 v ref this is the reference out put. it provides charging current for capacitor c t through resistor r t .
uc2843b preliminary linear integrated circuit unisonic technologies co., ltd 3 of 9 www.unisonic.com.tw qw-r103-048.a ? block diagram
uc2843b preliminary linear integrated circuit unisonic technologies co., ltd 4 of 9 www.unisonic.com.tw qw-r103-048.a ? absolute maximum rating (ta=25c, unless otherwise specified) parameter symbol ratings unit supply voltage (low impedance source) v cc 30 v analog input voltage (v fb and i sense ) v in -0.3~+6.3 v supply current i cc 30 ma output current i out 1 a error amplifier output sink current i o(sink) 10 ma power dissipation p d 702 mw output energy (capacitive load) w 5 j junction temperature t j 150 c operating temperature t opr -40~+85 c storage temperature t stg -65~+150 c notes: 1. 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. 2. all voltages are concerning the device gnd terminal. ? thermal data parameter symbol min typ max unit junction to ambient ja 178 c/w ? recommended operating conditions parameter symbol min typ max unit supply voltage v cc 30 v r t /c t 0 5.5 v input voltage vfb and i sense v in 0 5.5 v output voltage (output) v out 0 30 v supply current, externally limited i cc 25 ma output current i out 200 ma reference output current i o(ref) -20 ma oscillator frequency f osc 100 500 khz operating temperature ta -40 +85 c
uc2843b preliminary linear integrated circuit unisonic technologies co., ltd 5 of 9 www.unisonic.com.tw qw-r103-048.a ? electrical characteristics (v cc = 15 v, r t = 10k ? , c t = 3.3nf, t j =25c, unless otherwise specified) parameter symbol test conditions min typ max unit reference section reference output voltage v ref i out =1ma, t j =25c 4.95 5 5.05 v line regulation v out v cc = 12v~25v 6 20 mv load regulation v out i out = 1ma~20ma 6 25 mv average temperature coefficient of output voltage t s 0.2 0.4 mv/c total output variation v ref v cc =12v~25v, i out =1ma~20ma 4.9 5.1 v output noise voltage en f = 10hz~10khz, t j =25c 50 v long term stability t j =25c for 1000 hours 5 25 mv output short circuit current i sc -30 -100 -180 ma oscillator section t j =25c, r t =62k ? , c t =1nf, min =225 khz, max =275 khz 49 52 55 khz frequency f osc t j = full range 48 56 khz frequency change with voltage v f osc v cc = 12v ~ 25v 0.2 1 % frequency change with temperature t f osc t j = full range 5 % oscillator voltage swing v osc peak to peak 1.7 v t j =25c, r t /c t =2v 7.8 8.3 8.8 ma discharge current i disc r t /c t =2v 7.5 8.8 ma error-amplifier section voltage feedback input v fb comp =2.5v 2.45 2.5 2.55 v input bias current i i(bias) -0.3 -1 a open loop voltage gain g vo v out =2v~4v 65 90 db unity gain bandwidth g bw 0.7 1 mhz power supply rejection ratio psrr v cc =12v~25v 60 70 db output sink current i sink v fb =2.7v, comp=1.1v 2 6 ma output source current i source v fb =2.3v, comp =5v -0.5 -0.8 ma v oh v fb =2.3v, r l =15k ? to gnd 5 6 v output voltage swing high state v ol v fb =2.7v, r l =15k ? to gnd 0.7 1.1 v current-sense section current sense input voltage gain g v (note 2,3) 2.85 3 3.15 v/v maximum current sense input threshold v th comp =5v (note 2) 0.9 1 1.1 v power supply rejection ratio psrr v cc =12v~25v (note 2) 70 db input bias current i i(bias) -2 -10 a propagation delay t d v fb =0v~2v 150 300 ns output section i oh =-20ma 13 13.5 v high-level output voltage v oh i oh =-200ma 12 13.5 v i ol =20ma 0.1 0.4 v low-level output voltage v ol i ol =200ma 1.5 2.2 v under-voltage lockout output voltage v uvlo v cc =5v, i ol =1ma 0.7 1.2 v output voltage rise time t r c l =1nf, t j = 25c 50 150 ns output voltage fall time t f c l =1nf, t j = 25c 50 150 ns
uc2843b preliminary linear integrated circuit unisonic technologies co., ltd 6 of 9 www.unisonic.com.tw qw-r103-048.a ? electrical characteristics (cont.) parameter symbol test conditions min typ max unit undervoltage-lockout section startup threshold v th 7.8 8.4 9 v minimum operating voltage after start-up v cc(min) 7 7.6 8.2 v pulse-width modulator section maximum duty cycle d c(max) 94 96 100 % minimum duty cycle d c(min) 0 % supply voltage power startup supply current i cc +i c 0.3 0.5 ma power operating supply current i cc +i c v fb and i sense at 0v 11 17 ma power supply zener voltage v z i cc =25ma 30 34 v notes: 1. adjust v cc above the start threshold before setting it to 15v. 2. measured at the trip point of the latch, with vfb at 0v. 3. measured between i sense and comp, with the input changing from 0v ~ 0.8v.
uc2843b preliminary linear integrated circuit unisonic technologies co., ltd 7 of 9 www.unisonic.com.tw qw-r103-048.a ? application information error amplifier (ea) configuration circuit: z1 z2 v fb comp 0.5ma 2.5v error amplifier ea note: error amplifier can source or sink up to 0.5ma. current-sense circuit: notes: 1. peak current (i s ) is determined by the formula: i s(max) = 1 v/r s 2. a small rc filter formed by resistor r f and capacitor c f may be required to suppress switch transients. the oscillator frequency is set using the circuit: v ref r t /c t gnd c t r t the frequency is calculated as followed: f = 1 / r t c t for r t > 5k ? : f = 1.72 / r t c t
uc2843b preliminary linear integrated circuit unisonic technologies co., ltd 8 of 9 www.unisonic.com.tw qw-r103-048.a ? application information(cont.) open-loop laboratory test fixture in the open-loop laboratory test fixture, high peak cu rrents and loads need grounding techniques. the transistor and 5-k ? potentiometer sample the oscillator waveform, applying an adjustable ramp to the i sense terminal. timing and bypass capacitors should be connected closely to the gnd terminal in a single-point ground. shutdown technique the pwm controller can be shut down through two me thods: the one is raising voltage (above 1 v) at i sense , the other is pulling the comp terminal below a voltage two diode drops above ground. either method can leave the output of the pwm comparator high (refe r to block diagram). to reset the pwm latch is dominant so the output can stay low in the case of the next cl ock cycle is coming and the comp or i sense terminal is removed beyond this shutdown condition. for example, an externally-latch ed shutdown can be accomplished by adding an scr reset by cycling v cc below the lower uvlo threshold. so the referenc e turns off then allows the scr to reset at this condition. v ref i sense 330 1k 500 to current-sense resistor shutdown comp
uc2843b preliminary linear integrated circuit unisonic technologies co., ltd 9 of 9 www.unisonic.com.tw qw-r103-048.a ? application information(cont.) shutdown technique (cont.) a fraction of the triangular-wave osc illator can be summed resistively with the current-sense signal providing slope compensation for converters, which requiring duty cycles over 50%. please note that capacitor c forms a filter with r2 to suppress the leading-edge switch spikes. c t r t r 1 r 2 c r sense i sense 0.1f v ref i sense r t /c t 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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