DESCRIPTION
TheUC3842/3/4/5family of controlICs provides the necessary features to implement off-line or DC to DC fixed frequency current mode control schemes with a minimal externalparts count.Internallyimplementedcircuits include undervoltagelockout featuring start-up current less than 1 mA, a precision reference trimmed for accuracy at the error amp input, logic to insure latched operation, a PWM comparatorwhich also providescurrentlimit 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 theoff-state. Differences between members of this family are the under-voltage lockout thresholds and maximum duty cycle ranges. A range of the zero to < 50 % is obtained by the UC3844 and UC3845 by the additionof an internal toggle flip flop which blanks the output off every other clock cycle. BLOCK DIAGRAM (toggle flip flop used only in U3844 and UC3845) October 1998 1/11 UC2842/3/4/5-UC3842/3/4/5...
STMicroelectronics
