UC3842 Просмотр технического описания (PDF) - Philips Electronics
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UC3842 Datasheet PDF : 8 Pages
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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 3
RT/CT 4
8 VREF
7 VCC
6 OUTPUT
5 GROUND
TOP VIEW
D Package
COMP 1
NC 2
VFB 3
NC 4
ISENSE 5
NC 6
RT/CT 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
6V
16V
2.5V
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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