UC3842A PDF Datasheet浏览和下载

型号.:
UC3842A
PDF下载:
下载PDF文件
内容描述:
高性能电流模式PWM控制器
[HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER]
文件大小:
131 K
文件页数:
15 Pages
品牌Logo:
品牌名称:
STMICROELECTRONICS [ STMICROELECTRONICS ]
PCB Prototype
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  • 操作
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®
UC2842A/3A/4A/5A
UC3842A/3A/4A/5A
HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER
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TRIMMED OSCILLATOR DISCHARGE CUR-
RENT
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 CURRENT (< 0.5mA)
DOUBLE PULSE SUPPRESSION
Minidip
SO8
DESCRIPTION
TheUC384xA family ofcontrolICs providesthe nec-
essary 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-
outfeaturingstart-up current less than0.5mA,a pre-
cision reference trimmed for accuracy at the error
amp input, logicto insure latched operation,a PWM
comparatorwhich alsoprovidescurrent limit control,
and a totem pole output stage designed to source
or sink high peakcurrent. The outputstage, suitable
for driving N-Channel MOSFETs, is low in the off-
state.
Differences between members of this family are the
under-voltagelockout thresholds and maximum duty
cycle ranges. The UC3842A and UC3844A have
UVLO thresholds of 16V (on) and 10V (off), ideally
suitedoff-lineapplicationsThecorrespondingthresh-
olds for the UC3843A and UC3845A are 8.5 V and
7.9V. The UC3842A and UC3843A can operate to
dutycycles approaching100%.A range of the zeroto
< 50 % is obtainedby theUC3844Aand UC3845Aby
the addition of an internal toggle flip flopwhich blanks
the output off every otherclock cycle.
BLOCK DIAGRAM
(toggle flip flop used only in UC3844A and UC3845A)
Vi
7
34V
GROUND
5
UVLO
S/R
5V
REF
INTERNAL
BIAS
VREF GOOD
LOGIC
RT/CT
4
OSC
ERROR AMP.
2R
R
1V
T
8
VREF
5V 50mA
2.50V
6
OUTPUT
VFB
COMP
CURRENT
SENSE
2
1
3
+
-
S
R
CURRENT
SENSE
COMPARATOR
PWM
LATCH
UC3842A
D95IN331
March 1999
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