1 FEATURES
■ TRIMMED OSCILLATOR DISCHARGE
CURRENT
■ 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 CURRENT (< 0.5mA)
DOUBLE PULSE SUPPRESSION

2 DESCRIPTION
The UC384xA 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 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 off-state.
Differences between members of this family are
the under-voltage lockout thresholds and maximum duty cycle ranges. The UC3842A and
UC3844A have UVLO thresholds of 16V (on) and
10V (off), ideally suited off-line applications The
corresponding thresholds for the UC3843A and
UC3845A are 8.5 V and 7.9V. The UC3842A and
UC3843A can operate to duty cycles approaching
100%. A range of the zero to < 50 % is obtained by
the UC3844A and UC3845A by the addition of an
internal toggle flip flop which blanks the output off
every other clock cycle.