參數(shù)資料
型號(hào): UC2845BD1
廠商: ON SEMICONDUCTOR
元件分類: 穩(wěn)壓器
英文描述: HIGH PERFORMANCE CURRENT MODE CONTROLLERS
中文描述: 1 A SWITCHING CONTROLLER, 275 kHz SWITCHING FREQ-MAX, PDSO8
封裝: SOIC-8
文件頁(yè)數(shù): 1/15頁(yè)
文件大?。?/td> 135K
代理商: UC2845BD1
UC2842B/3B/4B/5B
UC3842B/3B/4B/5B
March1999
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
UNDERVOLTAGELOCKOUT
.
HIGH CURRENT TOTEM POLEOUTPUT
.
UNDERVOLTAGE LOCKOUT WITH HYSTER-
ESIS
.
LOWSTART-UPANDOPERATINGCURRENT
DESCRIPTION
TheUC384xBfamilyofcontrolICsprovidesthenec-
essary features to implement off-line or DC to DC
fixedfrequencycurrent modecontrolschemeswith
a minimal external parts count. Internally imple-
mentedcircuits includea trimmedoscillatorfor 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
comparatorwhichalsoprovidescurrentlimitcontrol,
and a totem pole output stage designed to source
orsinkhighpeakcurrent.Theoutputstage,suitable
for driving N-Channel MOSFETs, is low in the off-
state.
Differencesbetweenmembers of this family arethe
under-voltagelockoutthresholdsandmaximum duty
cycle ranges. The UC3842B and UC3844B have
UVLO thresholds of 16V (on) and 10V (off), ideally
suitedoff-lineapplicationsThecorrespondingthresh-
oldsfortheUC3843BandUC3845Bare8.5Vand7.9
V.TheUC3842BandUC3843Bcanoperateto duty
cyclesapproaching100%. A rangeof the zero to <
50 % is obtainedbythe UC3844Band UC3845Bby
theadditionofaninternaltoggleflipflopwhichblanks
theoutputoffeveryotherclockcycle.
BLOCK DIAGRAM
(toggle flip flop used only in UC3844B and UC3845B)
UVLO
S/R
5V
REF
34V
INTERNAL
BIAS
VREF GOOD
LOGIC
2.50V
T
S
R
OSC
R
1V
CURRENT
SENSE
COMPARATOR
2R
+
-
PWM
LATCH
7
5
4
2
1
3
8
6
ERROR AMP.
Vi
GROUND
RT/CT
VFB
COMP
CURRENT
SENSE
VREF
5V 50mA
OUTPUT
D95IN331
Minidip
SO8
UC3842B
1/15
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