UC3845B

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 COMPENSA- TION . LATCHING PWM FOR CYCLE-BY-CYCLE CURRENT LIMITING . INTERNALLY TRIMMED REFERENCE WITH UNDERVOLTAGE LOCKOUT . HIGH CURRENT TOTEM POLE OUTPUT . UNDERVOLTAGE LOCKOUT WITH HYSTER- ESIS . LOW START-UP AND OPERATING CURRENT DESCRIPTION The UC384xB 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 0.5mA, a precision reference trimmed for accuracy at the error amp input, logic to insure latched operation, a PWM Minidip SO8 comparator 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 UC3842B and UC3844B have UVLO thresholds of 16V (on) and 10V (off), ideally suited off-line applications The corresponding thresholds for the UC3843B and UC3845B are 8.5 V and 7.9 V. The UC3842B and UC3843B can operate t...