UC3844A high performance current mode controller l output deadtime adjustable from 50% to 70% l current mode operation to 500 khz l automatic feed forward compensation l latching pwm for cycleCbyCcycle current limiting l internally trimmed reference with undervoltage lockout l high current totem pole output l undervoltage lockout with hysteresis l low startup and operating current cs suffix plastic package sop-14 the UC3844A series of high performance fixed frequency current mode controllers are specifically designed for offCline and dcCtoCdc converter applications offering the designer a cost effective solution with minimal external components. this integrated circuit features an oscillator, a temperature compensated reference, high gain error amplifier, current sensing comparator, and a high current totem pole output ideally suited for driving a power mosfet. also included are protective features consisting of input and reference undervoltage lockouts each with hysteresis, cycleCbyCcycle current limiting, a latch for single pulse metering, and a flip-flop which blanks the output off every other oscillator cycle, allowing output deadtimes to be programmed for 50% to 70%. this device is available in an 8Cpin dualCinC line plastic package as well as the 14Cpin plastic sur- face mount (sopC14). the sopC14 package has sepa- rate power and ground pins for the totem pole output stage. the UC3844A has uvlo thresholds of 16v (on) and 10v (off), ideally suited for off-line converters. cd suffix plastic package 8 dip pin connections simplified block diagram pin numbers adjacent to terminals are for the d suffix 8-dip package. pin numbers in parenthesis are for the s suffix sopC14 package. notes: 1. maximum package power dissipation limits must be observed. 2. adjust v cc above the startup threshold before setting to 15 v. 3. low duty cycle pulse techniques are used during test to maintain junction temperature as close to ambient as possible t low = 0 c, t high = +70 c. 4. this parameter is measured at the latch trip point with v fb = 0v. 5. comparator gain is defined as: a v d v output compensation d v current sense input d8 suffix plastic package 8 sop
UC3844A high performance current mode controller total power supply and zener current (i cc +i z )30ma output current, source or sink (note 1) i o 1.0 a output energy (capacitive load per cycle) w 5.0 m j current sense and voltage feedback inputs v in -0.3 to +5.5 v error amp output sink current i o 10 ma power dissipation and thermal characteristics cs, d8 suffix, sop-14, sop-8 package maximum power dissipation p d 862 mw thermal resistance, junction to air r q ja 145 o c/w cd suffix, 8-dip package maximum power dissipation p d 1.25 w thermal resistance, junction to air r q ja 100 o c/w operating ambient temperature range t a 0 to 70 o c operating junction temperature t j 150 o c storage temperature range t s -65 to 150 o c item symbol rating unit absolute maximum ratings electrical characteristics item symbol min typ max unit reference output voltage (i o = 1.0ma, t j = 25 o c) v ref 4.9 5.0 5.1 v line regulation (v cc = 12v to 25v) reg line --- 2.0 20 mv load regulation (i o = 1.0ma to 20ma) reg load --- 3.0 25 mv temperature stability t s --- 0.2 --- mv/ o c total output variation over line, load, temp. v ref 4.82 --- 5.18 v output noise voltage (f = 10hz to 10khz, t j = 25 o c) v n --- 50 --- m v long term stability (t a = 125 o c for 1000 hours) s --- 5.0 --- mv output short circuit current isc -30 -85 -180 ma v cc = 15v (note 2), r t = 10k, ct = 3.3nf, t a = 0 to 70 o c (note 3) unless otherwise noted. reference section frequency f osc v t j = 25 o c475257 t a = 0 to 70 o c 46 --- 60 frequency change with voltage (v cc = 12v to 25v) d f osc / d v --- 0.2 1.0 % frequency change with temperature d f osc / d t --- 5.0 --- % oscillator voltage swing (peak-to-peak) v osc --- 1.6 --- v discharge current (v osc = 2.0v) i dischg ma t j = 25 o c --- 10.8 --- oscillator section
electrical characteristics item symbol min typ max unit voltage feedback input (v o = 2.5v) v fb 2.42 2.5 2.58 v input bias current (v fb = 2.7v) i ib --- -0.1 -2.0 m a open loop voltage gain (v o = 2.0v to 4.0v) a vol 65 90 --- db unity gain bandwidth (t j = 25 o c) bw 0.7 1.0 --- mhz power supply rejection ratio (v cc = 12v to 25v) psrr 60 70 --- db output current ma sink (v o = 1.1v, v fb = 2.7v) i sink 2.0 12 --- source (v o = 5.0v, v fb = 2.3v) i source -0.5 -1.0 --- output voltage swing v high state (r l = 15k to gnd, v fb = 2.3v) v oh 5.0 6.2 --- low state (r l = 15k to v ref , v fb = 2.3v) v ol --- 0.8 1.1 error amplifier section UC3844A high performance current mode controller current sense input voltage gain (notes 4 & 5) a v 2.85 3.0 3.15 v/v maximum current sense input threshold (note 4) v th 0.9 1.0 1.1 v power supply rejection ratio (v cc = 12v to 25v) psrr --- 70 --- db input bias current i ib --- -2.0 -10 m a propagation delay (current sense input to output) t plh(in/out) --- 150 300 n s current sense section output voltage v low state (i sink = 20ma) v ol --- 0.1 0.4 (i sink = 200ma) --- 1.6 2.2 high state (i sink = 20ma) v oh 13 13.5 --- (i sink = 200ma) 12 13.4 --- output voltage with uvlo activated v ol(uvlo) v (v cc = 6.0v, i sink = 1.0ma) --- 0.1 1.1 output voltage rise time (c l = 1.0nf, t j = 25 o c) t r --- 50 150 n s output voltage fall time (c l = 1.0nf, t j = 25 o c) t f --- 50 150 n s output section startup threshold v th 14.5 16 17.5 v minimum operating voltage after turn-on v cc(min) 8.5 10 11.5 v undervoltage lockout section duty cycle max. dc max 47 48 50 % min. dc min --- --- 0 pwm section power supply current (v cc = 14v) (note 2) i cc ma startup --- 0.17 0.3 operating --- 12 17 power supply zener voltage v z 30 36 --- v total device
UC3844A high performance current mode controller figure 1 - timing resistor versus oscillator frequency figure 2 - output deadtime versus oscillator frequency oscillator frequency (hz) timing resistor (k w ) oscillator frequency (hz) percent output deadtime figure 3 - error amp small signal transient response figure 4 - error amp large signal transient response figure 5 - error amp open-loop gain and phase versus frequency frequency (hz) open-loop voltage gain (db) excess phase (degrees) figure 6 - current sense input threshold versus error amp output voltage error amp output voltage (v) current sense input threshold (v)
UC3844A high performance current mode controller figure 8 - reference short circuit current versus temperature ambient temperature ( o c) reference short circuit current (ma) figure 7 - reference voltage change versus source current reference source current (ma) reference voltage change (mv) figure 9 - reference load regulation 2.0 ms/div output voltage change (2.0mv/div) figure 10 - reference line regulation 2.0 ms/div output voltage change (2.0mv/div) figure 11 - output saturation voltage versus load current output load current (ma) output saturation voltage (v) figure 12 - output waveform
UC3844A high performance current mode controller figure 14 - supply current versus supply voltage supply voltage (v) supply current (ma) figure 13 - output cross conduction supply current output voltage
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