UC1842/3/4/5

•Optimized For Off-line And DC To DC Converters
•Low Start Up Current (<1mA)
•Automatic Feed Forward Compensation
•Pulse-by-pulse Current Limiting
•Enhanced Load Response Characteristics
•Under-voltage Lockout With Hysteresis
•Double Pulse Suppression
•High Current Totem Pole Output
•Internally Trimmed Bandgap Reference
•500khz Operation
•Low RO Error Amp

The UC1842/3/4/5 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 under-voltage lockout featuring start up current less than 1mA, 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 UC1842 and UC1844 have UVLO thresholds of 16V (on) and 10V (off), ideally suited to off-line applications. The corresponding thresholds for the UC1843 and UC1845 are 8.4V and 7.6V. The UC1842 and UC1843 can operate to duty cycles approaching 100%. A range of zero to 50% is obtained by the UC1844 and UC1845 by the addition of an internal toggle flip flop which blanks the output off every other clock cycle.