UC3843B DESCRIPTION:
The UC3843B familyofcontrolICsprovidesthenecessary 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 eference 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 UC3843B have UVLO thresholds of 16V (on) and 10V (off), ideally
The 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. 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 |
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