BICMOS PWM CONTROLLERS
TC25C25
TC35C25
BENCH TEST OPERATIONAL SIMULATION
WAVEFORMS
3V
0.5V
5k
1
2
1
IN–
IN+
SYNC
OSC OUT
CT
RT
DISCH
SOFT
VREF
VIN
OUTB
VDD
GND
OUTA
SHDN
16
15
14
13
12
11
10
.1µf
MET
+
–
V011
16V
2
3
GND
4
5
MET
6
3.7k
CT
PIN 5
PIN 2
VOLTAGE
OSC OUT
PIN 4
DEAD TIME
1000pF
OUTPUT A
PIN 11
7
0 to 1k
8
3
4
5
6
7
1000
CMPTR 9
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
Although the pin-out and functions are the same for both
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 R
T
and C
T
values are
different for any particular frequency and dead-time require-
ment.
The most important difference is that the absolute
maximum rating of the V
DD
and V
IN
voltages for the TC35C25
is 18V, whereas the UC3525 is 40V.
TYPICAL CHARACTERISTICS
Oscillator Frequency
vs. Ct and Rt
900
800
700
VDD = VIN = 16V, TA +25°C
Rt = 1k
Rt = 2k
Rt = 5k
Rt = 10k
Rt = 20k
40
35
30
VDD = 16V, TA +25°C
Supply Current
vs. Frequency
3000
2500
Dead Time
vs. Ct and Discharge Resistor
VDD = 16V, TA +25°C, Rt = 10k
Ct = 1000pF
DEAD TIME (nsec)
CL = 2200pF
CL = 1000pF
CL = 470pF
CL = 10pF
FOSC (kHz)
600
500
400
300
200
100
0
200
400
600
Ct (pF)
IDD (mA)
25
20
15
10
5
2000
1500
1000
500
0
Ct = 500pF
Ct = 330pF
Ct = 100pF
800
1000
0
0
0.2
0.4
0.6
0.8
FREQUENCY (MHz)
1
0
200
400
600
800
DISCHARGE RESISTOR (Ω)
8
TELCOM SEMICONDUCTOR, INC.
4-117
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