深圳市广辉电子有限公司

特性：

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 TOTEMPOLEOUTPUT
UNDERVOLTAGE LOCKOUT WITH HYSTER-
ESIS
LOWSTART-UPANDOPERATINGCURRENT

描述：

DESCRIPTION
TheUC384xBfamilyofcontrol ICsprovidesthenec-
essary features to implement off-line or DC to DC
fixed frequencycurrent mode control schemes with
a minimal external parts count. Internally imple-
mented circuits includea trimmed oscillator for pre-
cise DUTY CYCLE CONTROL under voltage lock-
out featuringstart-upcurrent less than0.5mA,a pre-
cision reference trimmed for accuracy at the error
amp input, logicto insurelatchedoperation,a PWM
comparatorwhich alsoprovidescurrent limit control,
and a totempole output stage designed to source
or sink high peakcurrent.Theoutputstage,suitable
for driving N-Channel MOSFETs, is low in the off-
state.
Differences betweenmembers of this family are the
under-voltagelockout thresholdsandmaximumduty
cycle ranges. The UC3842B and UC3844B have
UVLO thresholds of 16V (on) and 10V (off), ideally
suitedoff-lineapplicationsThecorrespondingthresh-
oldsfortheUC3843BandUC3845Bare8.5Vand7.9
V. The UC3842B andUC3843B can operate to duty
cycles approaching 100%. A range of the zero to <
50 % is obtained by the UC3844Band UC3845Bby
theadditionofan internal toggleflip flopwhich blanks
the outputoff everyotherclock cycle

框图BLOCK DIAGRAM：

极限参数ABSOLUTE MAXIMUMRATINGS：

脚位：

开环电路测试Open Loop Test Circuit：