UC3843T datasheet, PDF - EEWORLD Datasheet

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UC3843T: DescriptionHIGH PERFORMANCE CURRENT MODE PWM CONTROLLER; File Size165KB，15 Pages; ManufacturerSTMicroelectronics; Websitehttp://www.st.com/

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UC3843T Overview

HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER

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UC3842T UC3843T

UC3844T UC3845T

HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER

TRIMMED OSCILLATOR FOR PRECISE FRE-

QUENCY CONTROL

OSCILLATOR FREQUENCY GUARANTEED

AT 250kHz

CURRENT MODE OPERATION TO 500kHz

AUTOMATIC FEED FORWARD COMPENSA-

TION

LATCHING PWM FOR CYCLE-BY-CYCLE

CURRENT LIMITING

INTERNALLY TRIMMED REFERENCE WITH

UNDERVOLTAGE LOCKOUT

HIGH CURRENT TOTEM POLE OUTPUT

UNDERVOLTAGE LOCKOUT WITH HYSTER-

ESIS

LOW START-UP AND OPERATING CURRENT

Minidip

SO8

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 imple-

mented circuits include a trimmed oscillator for pre-

cise DUTY CYCLE CONTROL under voltage lock-

out featuring start-up current less than 0.5mA, a pre-

cision 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 UC3842T and UC3844T have

UVLO thresholds of 16V (on) and 10V (off), ideally

suited to off-line applications The corresponding

thresholds for the UC3843T and UC3845T are 8.5 V

and 7.9 V. The UC3842T and UC3843T can operate

to duty cycles approaching 100%. 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)

34V

GROUND

UVLO

S/R

REF

INTERNAL

BIAS

VREF GOOD

LOGIC

RT/CT

OSC

ERROR AMP.

VREF

5V 50mA

2.50V

OUTPUT

VFB

COMP

CURRENT

SENSE

CURRENT

SENSE

COMPARATOR

D95IN331

PWM

LATCH

September 2001

1/15

UC3843T Related Products

	UC3843T	UC3842T	UC3842TD	UC3843TD	UC3844T	UC3844TD	UC3845T	UC3845TD
Description	HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER	HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER	HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER	HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER	HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER	HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER	HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER	HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER

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