UC3842B Datasheet | STMicroelectronics

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 PENSA- 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 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 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 to duty cycles approaching 100%. A range of the zero to < 50 % is obtained by the UC3844B and UC3845B 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 UC3844B and UC3845B) 7 Vi 5 GROUND 4 RT/CT 2...