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UC3842 Datasheet PDF - Philips

Part Number UC3842
Description Current-mode PWM controller
Manufacturers Philips 
Logo Philips Logo 



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UC3842 datasheet, circuit
Philips Semiconductors Linear Products
Current-mode PWM controller
Product specification
UC3842
DESCRIPTION
The UC3842 is available in an 8-Pin mini-DIP the necessary
features to implement off-line, fixed-frequency current-mode control
schemes with a minimal external parts count. This technique results
in improved line regulation, enhanced load response characteristics,
and a simpler, easier to design control loop. Topological advantages
include inherent pulse-by-pulse current limiting.
Protection circuitry includes built-in undervoltage lock-out and
current limiting. Other features include fully-latched operation, a 1%
trimmed bandgap reference, and start-up current less than 1mA.
These devices feature a totem-pole output designed to source and
sink high peak current from a capacitive load, such as the gate of a
power MOSFET. Consistent with N-channel power devices, the
output is low in the OFF-state.
FEATURES
Low start-up current (1mA)
Automatic feed-forward compensation
Pulse-by-pulse current limiting
Enhanced load response characteristics
Undervoltage lock-out with hysteresis
Double pulse suppression
High current totem-pole output
Internally-trimmed bandgap reference
400kHz operation, guaranteed min
PIN CONFIGURATIONS
N Package
COMP 1
VFB 2
ISENSE
RT/CT
3
4
8 VREF
7 VCC
6 OUTPUT
5 GROUND
TOP VIEW
D Package
COMP
NC
VFB
NC
ISENSE
NC
RT/CT
1
2
3
4
5
6
7
14 VREF
13 NC
12 VCC
11 VC
10 OUTPUT
9 GROUND
8 POWER GROUND
TOP VIEW
APPLICATIONS
Off-line switched mode power supplies
DC-to-DC converters UC3842
BLOCK DIAGRAM
(12)7
VCC
(9)5
GND
(7)4
RT/CT
34V UVLO
16V
2.5V
6V
OSC
S/R 5V
REF
INTERNAL
BIAS
(3)2
VFB
(1)1
COMP
CURRENT (5)3
SENSE
ERROR
AMP
+
NOTE:
Pin numbers in parentheses refer to the D package.
2R
R
S
R
1V
CURRENT
SENSE
COMPARATOR
PWM
LATCH
7(11)
8(14)
VREF
5.0V
50mA
6(10)
OUTPUT
5(8)
August 31, 1994
1100
853-0614 13721

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UC3842 equivalent
Philips Semiconductors Linear Products
Current-mode PWM controller
Product specification
UC3842
CURRENT SENSE CIRCUIT
IS
ERROR
AMP
R
RS
1
COMP
3
CURRENT
SENSE
5
GND
NOTE:
Peak current (IS) is determined by the formula:
1.0V
IS MAX + Rs
A small RC filter may be required to suppress switch transients.
TYPICAL PERFORMANCE CHARACTERISTICS
Output Saturation Characteristics
4
3
2
1
0
0.01
0.03 0.05 0.1
0.3 0.5 1.0
OUTPUT CURRENT, SOURCE OR SINK (A)
2R
R 1V
CURRENT
SENSE
COMPARATOR
Error Amplifier Open-Loop
Frequency Response
100 45
80 0
0
Av
60 –45
40 –90
20 –135
0 –180
–20 –225
10 100 1k 10k 100k 1M 10M
FREQUENCY (Hz)
August 31, 1994
1104

5 Page
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Information Total 8 Pages
Download[ UC3842.PDF Datasheet ]

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