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UC3845BD1 Datasheet

  • UC3845BD1

  • HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER

  • 137.29KB

  • 15页

  • STMICROELECTRONICS   STMICROELECTRONICS

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UC2842B/3B/4B/5B
UC3842B/3B/4B/5B
HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER
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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
TheUC384xB 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 UC3842B and UC3844B have
UVLO thresholds of 16V (on) and 10V (off), ideally
suitedoff-lineapplicationsThecorrespondingthresh-
oldsforthe UC3843BandUC3845Bare8.5 V and7.9
V. The UC3842B and UC3843B can operate to duty
cycles approaching 100%. A range of the zero to <
50 % is obtained by the UC3844B and UC3845B by
the addition of an internal toggle flip flopwhich blanks
the output off every otherclock cycle.
BLOCK DIAGRAM
(toggle flip flop used only in UC3844B and UC3845B)
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
UC3842B
D95IN331
March 1999
1/15

UC3845BD1 产品属性

  • 98

  • 集成电路 (IC)

  • PMIC - 稳压器 - DC DC 切换控制器

  • -

  • 电流模式

  • 1

  • 275kHz

  • 50%

  • 7.6 V ~ 30 V

  • 无

  • 是

  • 是

  • 是

  • 无

  • 无

  • 无

  • 是

  • 0°C ~ 70°C

  • 8-SOIC（0.154"，3.90mm 宽）

  • 管件

  • UC3845BD1OS

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