BICMOS PWM CONTROLLERS
1
2
3
4
5
6
7
8
TC25C25
TC35C25
BENCH TEST OPERATIONAL SIMULATION
WAVEFORMS
–
+
3V
1
2
3
4
5
6
7
8
IN
16
15
14
13
12
11
10
9
V
V
REF
IN
C
PIN 5
T
PIN 2
VOLTAGE
IN
0.5V
MET
OUT
SYNC
V011
+
B
–
GND
16V
V
.1µf
OSC OUT
DD
OSC OUT
PIN 4
DEAD TIME
C
T
GND
OUT
MET
R
T
A
1000pF
DISCH
SOFT
SHDN
OUTPUT A
PIN 11
0 to 1k
CMPTR
OUTPUT B
PIN 14
GND
The 5k potentiometer sets a reference voltage at pin 2.
When ramp voltage of pin 5 reaches this reference voltage,
output drive pulse is active ON. Varying the discharge
resistor will vary the dead time. Increasing the discharge
resistor will effect an increase in the dead time.
REPLACING BIPOLAR VERSIONS WITH CMOS
Althoughthepin-outandfunctionsarethesameforboth
the Bipolar and CMOS versions, there are several differ-
ences that need to be taken into account. The reference
voltage on the TC35C25 is 4V instead of 5V and the
oscillator ramp is 3V, not 4V. The RT and CT values are
different for any particular frequency and dead-time require-
ment.
The most important difference is that the absolute
maximumratingoftheVDD andVIN voltagesfortheTC35C25
is 18V, whereas the UC3525 is 40V.
TYPICAL CHARACTERISTICS
Oscillator Frequency
vs. C and R
Supply Current
vs. Frequency
Dead Time
vs. C and Discharge Resistor
t
t
t
3000
2500
2000
1500
1000
500
40
35
30
25
20
15
10
5
900
800
700
600
500
400
300
200
100
0
V
= V = 16V, T +25°C
V
= 16V, T +25°C
V
= 16V, T +25°C, R = 10k
DD A t
DD
IN
A
DD
A
R = 1k
t
C
C
C
C
= 2200pF
= 1000pF
= 470pF
= 10pF
C = 1000pF
t
L
L
L
L
R = 2k
t
C = 500pF
t
R = 5k
t
C = 330pF
t
R = 10k
t
R = 20k
t
C = 100pF
t
0
0
200
400
600
800
1000
0
0.2
0.4
0.6
0.8
1
0
200
400
600
800
1000
C (pF)
FREQUENCY (MHz)
DISCHARGE RESISTOR (Ω)
t
TELCOM SEMICONDUCTOR, INC.
4-117
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
