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UC3842A/UC3843A
SMPS Controller
Features
•
•
•
•
•
•
•
Low Start Current 0.2mA (typ)
Operating Range Up To 500KHz
Cycle by Cycle Current Limiting
Under Voltage Lock Out With Hysteresis
Short Shutdown Delay Time: typ.100ns
High Current Totem-pole Output
Output Swing Limiting: 22V
Description
The UC3842A/UC3843A are fixed PWM controller for Off-
Line and DC to DC converter applications. The internal cir-
cuits include UVLO, low start up current circuit, tempera-
ture compensated reference, high gain error amplifier,
current sensing comparator, and high current totem-pole out-
put for driving a POWER MOSFET. Also UC3842A/
UC3843A provide low start up current below 0.3mA and
short shutdown delay time typ. 100ns. The UC3842A has
UVLO threshold of 16V(on) and 10V(off). The UC3843A is
8.4V(on) and 7.6V(off). The UC3842A and UC3843A can
operate within 100% duty cycle.
8-DIP
1
8-SOP
1
Internal Block Diagram
7
V
CC
29V
V
REF
8
Internal
Bias
1/2V
REF
5V
V
REF
SET/
RESET
UVLO
5
GND
Good LOGIC
7
PWR
V
C
V
FB
2
Error Amp
+
-
C.S
PWM
Comp. LATCH
1/3
1V
S
R
22V
6
OUTPUT
COMP
1
5
PWR
C.S
3
R
T
/C
T
4
T
GND
OSCILLATOR
Rev. 5.0
©2000 Fairchild Semiconductor International
FAIRCHILD [ FAIRCHILD SEMICONDUCTOR ]
