
4-101
TELCOM SEMICONDUCTOR, INC.
7
6
5
4
3
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2
8
FUNCTIONAL BLOCK DIAGRAM
GENERAL DESCRIPTION
The TC38C46 is a current mode CMOS PWM control
IC. It draws only 2 mA supply current, so it can be driven
without a costly 50-60 Hz transformer. The output drive
stage is capable of high drive currents, 300mA typical.
The TC38C46 is pin compatible with earlier bipolar
products so that designers can easily update older designs.
A number of improvements have been added.
This second generation part has been designed with an
isolated drive stage. Unlike its cousin, the TC170, the output
stage of the TC38C46 can be run from a separate power
supply such as a secondary winding on an output trans-
former. This allows for bootstrap start-up of the power
supply.
CMOS CURRENT MODE PWM CONTROLLER
FEATURES
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Isolated Output Drive
Low Power CMOS Construction
Low Supply Current .................................2mA Typ.
Wide Supply Voltage Operation ..............8V to 18V
Latch-Up Immunity ................... 500mA on Outputs
Above and Below Rail Input Protection .............6V
High Output Drive ................................500mA Peak
Current Mode Control
Fast Rise/Fall Time .....................50nsec @ 1000pF
High Frequency Operation ..........................500kHz
UV Hysteresis Guaranteed
Programmable Current Limit
Shutdown Pin Available
Double Ended
Soft Start
Low Prop Delay Current Amp
to Output ......................................... < 350nsec Typ.
Low Prop Delay Shutdown
to Output ......................................... < 400nsec Typ.
TC38C46Pin Compatible with Unitrode UC3846
ESD Protected.................................................
±
2 kV
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+
–
+
–
+VS
+
+
–
.65V
– +
+
POSITIVE
FEEDBACK
–
D
C
Q
Q
100
μ
A
PWM
COMPARATOR
LIMIT BUFFER
AMPLIFIER
LOCK-UP
AMPLIFIER
CURRENT SENSE
AMPLIFIER
–
x3
ERROR
AMPLIFIER
350mV
Q1
Q2
3.5k
350mV
6k
SHUTDOWN
COMPARATOR
SHUTDOWN
CURRENT LIMIT
SOFT START ADJUST
TC38C46 OUTPUTS
LOW IN OFF STATE
OUTPUT A
GROUND
OUTPUT B
PWM LATCH
VIN
RT
CT
SYNC
– CURRENT
SENSE INPUT
+ ERROR
AMP INPUT
– ERROR
AMP INPUT
+ CURRENT
SENSE INPUT
COMPENSATION
Q3
VREF
2
12
14
1
16
11
13
15
9
8
10
3
4
7
5
6
TC18C46
TC28C46
TC38C46
Q4
+
–
+
5.1 VOLT
REFERENCE
UNDER VOLTAGE
LOCKOUT
OSCILLATOR
S
S
Q
R
ORDERING INFORMATION
Part No.
Configuration
Pkg./Temperature
TC18C46MJE
Non-Inverting
16-Pin CerDIP
– 55
°
C to +125
°
C
16-Pin SOIC (Wide)
– 40
°
C to +85
°
C
TC28C46EOE
Non-Inverting
TC28C46EPE
Non-Inverting
16-Pin Plastic DIP (Narrow)
– 40
°
C to +85
°
C
16-Pin SOIC (Wide)
0
°
C to +70
°
C
16-Pin Plastic DIP (Narrow)
0
°
C to +70
°
C
TC38C46COE
Non-Inverting
TC38C46CPE
Non-Inverting
TC18/28/28/C46-8 9/23/96
TC18C46
TC28C46
TC38C46