DESCRIPTION
The UC384XT 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 offstate. Differences between members of this family are the under-voltage lockout thresholds and maximum duty cycle ranges. A range of zero to < 50 % is obtained by the UC3844T and UC3845T 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 UC3844T and UC3845T) Vi 7 34V GROUND 5 UVLO S/R 5V REF INTERNAL BIAS VREF GOOD LOGIC RT/CT 4 OSC ERROR AMP.
STMicroelectronics
