UC3843T Datasheet | STMicroelectronics

.. ® UC3842T UC3843T UC3844T UC3845T HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER - . . . . 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 DESCRIPTION The UC384XT family of control ICs provides the necessary Features to implement off-line or DC to DC fixed frequency current mode control schemes with a minimal external parts count. Internally implemented circuits include a trimmed oscillator for precise DUTY CYCLE CONTROL under voltage lockout featuring start-up current less than 0.5m A, a precision reference trimmed for accuracy at the error amp input, logic to insure latched operation, a PWM parator which also provides current limit control, and a totem pole output stage designed to source or sink high peak current. The output stage, suitable for driving N-Channel MOSFETs, is low in the offstate. Differences between members of this family are the under-voltage lockout thresholds and maximum duty cycle ranges. The UC3842T and UC3844T have UVLO thresholds of 16V (on) and 10V (off), ideally suited to off-line applications The corresponding thresholds for the UC3843T and UC3845T are 8.5 V and 7.9 V. The UC3842T and UC3843T can operate to duty cycles approaching 100%. A range of zero to < 50 % is obtained by the UC3844T and UC3845T by the addition of an internal toggle flip flop which blanks the output off every other clock cycle. BLOCK DIAGRAM (toggle flip flop used only in UC3844T and UC3845T) 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 VREF 5V 50m A 2.50V OUTPUT VFB P CURRENT SENSE 2 1 3 + - S R CURRENT SENSE PARATOR D95IN331 PWM...