UC2843B Datasheet | STMicroelectronics

DESCRIPTION under-voltagelockout thresholds and maximum duty The UC384x B family ofcontrol ICs providesthe neccycle ranges. The UC3842B and UC3844B have essary features to implement off-line or DC to DC UVLO thresholds of 16V (on) and 10V (off), ideally fixed frequency current mode control schemes .. with suitedoff-lineapplications Thecorrespondingthresha minimal external parts count. Internally impleoldsforthe UC3843Band UC3845Bare8.5 V and7.9 mented circuits include a trimmed oscillator for pre V. The UC3842B and UC3843B can operate to duty cycles approaching 100%. A range of the zero to < cise DUTY CYCLE CONTROL under voltage lockoutfeaturingstart-up current less than0.5m A,a pre50 % is obtained by the UC3844B and UC3845B by cision reference trimmed for accuracy at the error the addition of an internal toggle flip flopwhich blanks amp input, logicto insure latched operation,a PWM the output off every otherclock cycle. BLOCK DIAGRAM (toggle flip flop used only in UC3844B and UC3845B) Vi 7 34V GROUND 5 UVLO S/R 5V REF INTERNAL BIAS VREF GOOD LOGIC RT/CT 4 OSC ERROR AMP. 2R R 1V T - . . . . TRIMMED OSCILLATOR FOR PRECISE FREQUENCY CONTROL OSCILLATOR FREQUENCY GUARANTEED AT 250k Hz CURRENT MODE OPERATION TO 500k Hz AUTOMATIC FEED FORWARD PENSATION LATCHING PWM FOR CYCLE-BY-CYCLE CURRENT LIMITING INTERNALLY TRIMMED REFERENCE WITH UNDERVOLTAGE LOCKOUT HIGH CURRENT TOTEM POLE OUTPUT UNDERVOLTAGE LOCKOUT WITH HYSTERESIS LOW START-UP AND OPERATING CURRENT Minidip SO8 VREF 5V 50m A 2.50V OUTPUT VFB P CURRENT SENSE 2 1 3 + - S R CURRENT SENSE PARATOR PWM LATCH UC3842B D95IN331 March 1999 1/15 UC2842B/3B/4B/5B - UC3842B/3B/4B/5B ABSOLUTE MAXIMUM RATINGS Symbol Vi Vi IO EO Parameter Supply Voltage (low impedance source) Supply Voltage (Ii < 30m A) Output Current Output Energy (capacitive load) Analog Inputs (pins 2, 3) Error Amplifier Output Sink Current Ptot Ptot Tstg TJ TL Power Dissipation at Tamb ≤ 25 °C (Minidip) Power Dissipation at Tamb ≤ 25 °C (SO8)...