3-299

TELCOM SEMICONDUCTOR, INC.

7

6

5

4

3

1

2

8

VOLTAGE-TO-FREQUENCY/

FREQUENCY-TO-VOLTAGE CONVERTERS

TC9400

TC9401

TC9402

In some cases, however, the TC9400 output must be

zero at power-on without a frequency input. In such cases,

sufficient to pulse the TC9400 and provide a power-on reset

(see Figure 11A). Where predictable power-on operation is

critical, a more complicated circuit, such as Figure 11B, may

be required.

VDD

14

11

1000pF

THRESHOLD

DETECTOR

1k

Ω

fIN

VDD

100k

Ω

1

µF

3

4

8

6

fIN

1

2

5

16

VCC

B

R

C

Q

VSS

A

CLRA

CD4538

(A)

(B)

TC9400

To TC 9400

Figure 11.

Power-On Operation/Reset

F/V POWER-ON RESET

In F/V mode, the TC9400 output voltage will occasion-

ally be at its maximum value when power is first applied. This

frequency-measurement applications this is not a problem,

because proper operation begins as soon as the frequency

input is applied.