Datasheet > UC3845TN

UC3845TN

更新时间： 2024-11-22 23:38:59

品牌	Logo	应用领域
其他 - ETC		模拟IC
页数	文件大小	规格书
15页	133K
描述
Analog IC

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中文翻译

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数据手册

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UC3845TN 数据手册

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

Minidip

SO8

LATCHING PWM FOR CYCLE-BY-CYCLE

CURRENT LIMITING

INTERNALLY TRIMMED REFERENCE WITH

UNDERVOLTAGE LOCKOUT

HIGH CURRENT TOTEM POLE OUTPUT

UNDERVOLTAGE LOCKOUT WITH HYSTER-

ESIS

comparatorwhichalsoprovidescurrentlimitcontrol,

and a totem pole output stage designed to source

orsinkhighpeakcurrent.Theoutputstage,suitable

for driving N-Channel MOSFETs, is low in the off-

state.

LOW START-UPAND OPERATINGCURRENT

Differencesbetween members of this family are the

under-voltagelockoutthresholdsandmaximum duty

cycle ranges. The UC3842T and UC3844T have

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

suited to off-line applications The corresponding

thresholdsfor the UC3843T and UC3845Tare 8.5 V

and 7.9V. The UC3842Tand UC3843Tcanoperate

to dutycycles approaching100%.A rangeof zeroto

<50 %isobtainedbytheUC3844TandUC3845Tby

theadditionofan internaltoggleflipflopwhichblanks

theoutputoff everyotherclock cycle.

DESCRIPTION

The UC384XT family of control ICs provides the

necessary features to implement off-line or DC to

DC fixed frequency current mode controlschemes

witha minimalexternalpartscount.Internallyimple-

mentedcircuits includea trimmed oscillator for pre-

cise DUTY CYCLE CONTROL under voltagelock-

outfeaturingstart-upcurrentlessthan0.5mA,a pre-

cision reference trimmed for accuracy at the error

ampinput,logicto insurelatchedoperation,a PWM

BLOCK DIAGRAM (toggle flip flop used only in UC3844T and UC3845T)

UVLO

34V

REF

VREF

5V 50mA

S/R

GROUND

INTERNAL

BIAS

2.50V

VREF GOOD

LOGIC

OUTPUT

RT/CT

OSC

ERROR AMP.

VFB

PWM

LATCH

COMP

CURRENT

SENSE

CURRENT

SENSE

COMPARATOR

D95IN331

1/15

September 2001

12 3 4 5 6 7...15

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