TC170 Ver la hoja de datos (PDF) - TelCom Semiconductor, Inc

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componentes Descripción

Fabricante

TC170

CMOS CURRENT MODE PWM CONTROLLER

TelCom Semiconductor, Inc 

CMOS CURRENT MODE

PWM CONTROLLER

1

TC170

VDD

1

2

FO

PIN 8

2.3V 4.3V

ICHARGE

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 RO = 24kΩ and

50

CO = 1000pF is:

45

[ ] FO =

1.27 2800

ROCO – RO2CO

CO

CO + 150 × 10–12

40

35

TA = +25°C

5

30

where: RO = Oscillator Resistor (Ω)

CO = Oscillator Capacitor (F)

25

FO = 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 [CO]

1 – 2.3

RO

Figure 7. Oscillator Frequency vs Oscillator Resistance

where: RO = Oscillator Resistor (kΩ)

7

CO = Oscillator Capacitor (pF)

TD = Output Dead Time (sec)

Maximum possible duty cycle is set by the dead time.

TELCOM SEMICONDUCTOR, INC.

8

4-125

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