UC3842BN Electronic IC Chip HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER

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UC2842B/3B/4B/5B

UC3842B/3B/4B/5B

HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER

. TRIMMED OSCILLATOR FOR PRECISE FREQUENCY CONTROL

. OSCILLATOR FREQUENCY GUARANTEED AT 250kHz

. CURRENT MODE OPERATION TO 500kHz

. AUTOMATIC FEED FORWARD COMPENSATION

. 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

DESCRIPTION

TheUC384xBfamilyofcontrolICsprovidesthenecessary features to implement off-line or DC to DC fixed frequencycurrent mode control schemes with a minimal external parts count. Internally implemented circuits includea trimmed oscillator for precise DUTY CYCLE CONTROL under voltage lockoutfeaturingstart-upcurrentless than0.5mA,a precision reference trimmed for accuracy at the error amp input,logicto insurelatchedoperation,a PWM comparatorwhich alsoprovidescurrentlimit control, and a totem pole output stage designed to source or sink high peakcurrent.Theoutputstage,suitable for driving N-Channel MOSFETs, is low in the offstate.

Differences between members of this family are the under-voltagelockout thresholdsand maximum duty cycle ranges. The UC3842B and UC3844B have UVLO thresholds of 16V (on) and 10V (off), ideally suitedoff-lineapplicationsThecorrespondingthresholdsfortheUC3843BandUC3845Bare8.5Vand7.9 V. The UC3842B and UC3843B can operateto duty cycles approaching 100%. A range of the zero to < 50 % is obtainedby the UC3844Band UC3845Bby theadditionofan internaltoggleflip flopwhich blanks the outputoff everyotherclock cycle.

ABSOLUTE MAXIMUM RATINGS

* All voltages are with respect to pin 5, all currents are positive into the specified terminal.

BLOCK DIAGRAM (toggle flip flop used only in UC3844B and UC3845B)

PIN CONNECTION (top view)