UC2842B/3B/4B/5B
®
UC3842B/3B/4B/5B
HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER
. TRIMMED OSCILLATOR FOR PRECISE FR...
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 UNDER
VOLTAGE LOCKOUT
. HIGH CURRENT TOTEM POLE OUTPUT . UNDER
VOLTAGE 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...