TC170 Datasheet, PDF (7/8 Pages) TelCom Semiconductor, Inc – CMOS CURRENT MODE PWM CONTROLLER

CMOS CURRENT MODE
PWM CONTROLLER
1
TC170
VDD
1
2
FO
PIN 8
2.3V 4.3V
I_CHARGE
2.3V
RO
8
9
10
SYNC
RO
1 mA
DISCHARGE
CO
CURRENT
2.3V
ON-TIME
PIN 10
OUTPUT DEAD TIME (TD)
3
4
Figure 6 . Oscillator Circuit
Oscillator Frequency and Output Dead Time
The oscillator frequency for R_O = 24kΩ and
50
C_O = 1000pF is:
45
[ ] ^{FO =}
1.27 2800
R_OC_O ^– R_O2C_O
C_O
C_O + 150 × 10^–12
40
35
TA = +25°C
5
30
where: R_O = Oscillator Resistor (Ω)
C_O = Oscillator Capacitor (F)
25
F_O = Oscillator Frequency (Hz)
20
250pF
15
The oscillator resistor can range from 5 kΩ to 50 kΩ.
Oscillator capacitor can range from 250 pF to 1000 pF.
10
500pF
6
Figure 7 shows typical operation for various resistance and
5
capacitance values.
1000pF 750pF
During transitions between the two outputs, simulta-
0 20 40 60 80 100 120 140 160 180 200
neous conduction is prevented. Oscillator fall time controls
OSCILLATOR FREQUENCY (kHz)
the output off, or dead time (Figure 6).
Dead time is approximately:
( ^{) TD =}
2000 [C_O]
1 – ^2.3
R_O
Figure 7. Oscillator Frequency vs Oscillator Resistance
where: R_O = Oscillator Resistor (kΩ)
7
C_O = Oscillator Capacitor (pF)
T_D = Output Dead Time (sec)
Maximum possible duty cycle is set by the dead time.
TELCOM SEMICONDUCTOR, INC.
8
4-125