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UC3842

ST Microelectronics
Part Number UC3842
Manufacturer ST Microelectronics
Description CURRENTMODE PWM CONTROLLER
Published May 23, 2005
Detailed Description ® UC2842/3/4/5 UC3842/3/4/5 CURRENT MODE PWM CONTROLLER . . . . . . . . . . . OPTIMIZED FOR OFF-LINE AND DC TO DC CON...
Datasheet PDF File UC3842 PDF File

UC3842
UC3842

Overview
® UC2842/3/4/5 UC3842/3/4/5 CURRENT MODE PWM CONTROLLER .
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OPTIMIZED FOR OFF-LINE AND DC TO DC CONVERTERS LOW START-UP CURRENT (< 1 mA) 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 500 KHz OPERATION LOW RO ERROR AMP Minidip SO14 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.
The UC3842 and UC3844 have UVLO thresholds of 16V (on) and 10V (off), ideally suited off-line applications The corresponding thresholds for the UC3843 and UC3845 are 8.
5 V and 7.
9 V.
The UC3842 and UC3843 can operate to duty cycles approaching 100%.
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 ABSOLUTE MAXIMUM RATINGS Symbol Vi Vi IO EO Parameter Supply Voltage (low impedance source) Supply Voltage (Ii < 30mA) Output Current Output Energy (capacitive load) Analog Inputs (pins 2, 3) Error Amplifier Output Sink Current Ptot Ptot Tstg TL Power Dissipation at Tamb ≤ 50 °C (minidip, DIP-14) ...


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