The XD/XL384x 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 lock-out 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 3842 and 3844 have UVLO thresholds of 16V (on) and 10V (off), ideally suited off-line applications The corresponding thresholds for the 3843 and 3845 are 8.5 V and 7.9 V. The 3842 and 3843 can operate to duty cycles approaching 100%. A range of the zero to < 50 % is obtained by the 3844 and 3845 by the addition of an internal toggle flip flop which blanks the output off every other clock cycle.
