Texas Instruments UC1842 3-4-5 Data Sheet

UC1842/3/4/5 UC2842/3/4/5 UC3842/3/4/5

Current Mode PWM Controller

FEATURES DESCRIPTION Optimized For Off-line And DC The UC1842/3/4/5 family of control ICs provides the necessary features to

To DC Converters implement off-line or DC to DC fixed frequency current mode control schemes

with minimal external parts count. Internally implemented circuits include

Low Start Up Current (<1m A)

under-voltage lockout featuring start up current less than 1m A, precision

Automatic Feed Forward reference trimmed for accuracy at the error amp input, logic to insure latched Compensation operation, PWM comparator which also provides current limit control, and

totem pole output stage designed to source or sink high peak current. The

Pulse-by-pulse Current Limiting

output stage, suitable for driving Channel MOSFETs, is low in the off state.

Enhanced Load Response

Differences between members of this family are the under-voltage lockout

Characteristics

thresholds and maximum duty cycle ranges. The UC1842 and UC1844 have

Under-voltage Lockout With UVLO thresholds of 16V (on) and 10V (off), ideally suited to off-line Hysteresis applications. The corresponding thresholds for the UC1843 and UC1845 are

8.4V and 7.6V. The UC1842 and UC1843 can operate to duty cycles

Double Pulse Suppression

approaching 100%. range of zero to 50% is obtained by the UC1844 and

High Current Totem Pole UC1845 by the addition of an internal toggle flip flop which blanks the output Output off every other clock cycle.

Internally Trimmed Bandgap Reference

500khz Operation

Low RO Error Amp

BLOCK DIAGRAM

1: A/BNote DIL-8 Pin Number. SO-14 and CFP-14 Pin Number.

Note 2: Toggle flip flop used only in and 1845.

SLUS223A APRIL REVISED MAY