3-291

TELCOM SEMICONDUCTOR, INC.

7

6

5

4

3

1

2

8

Figure 1.

10 Hz to 10 kHz V/F Converter

–

+

+5V

+5V

14

V

DD

+5V

RL

10k

Ω

RL

10k

Ω

8

10

9

fOUT

fOUT/2

11

3

µsec

DELAY

SELF-

START

12

5

20k

Ω

60pF

OpAmp

CINT

820pF

CREF

180pF

12pF

RIN

1M

Ω

VIN

INPUT

+5V

–5V

50k

Ω

510k

Ω

10k

Ω

3

1

OFFSET

ADJUST

IIN

ZERO

ADJUST

0V –10V

IBIAS

VSS

4

–5V

2

OUTPUT

COMMON

VREF OUT

RBIAS

100k

Ω

AMP OUT

TC9400

TC9401

TC9402

GND

6

THRESHOLD

DETECTOR

THRESHOLD

DETECT

REFERENCE

VOLTAGE

(TYPICALLY –5V)

÷2

VREF

7

–3V

This dissipates the charge stored on the reference capaci-

tor, so that when the output again crosses zero the system

is ready to recycle. In this manner, the continued discharg-

ing of the integrating capacitor by the input is balanced out

by fixed charges from the reference voltage. As the input

voltage is increased, the number of reference pulses re-

quired to maintain balance increases, which causes the

output frequency to also increase. Since each charge in-

crement is fixed, the increase in frequency with voltage is

linear. In addition, the accuracy of the output pulse width

does not directly affect the linearity of the V/F. The pulse

must simply be long enough for full charge transfer to take

place.

VOLTAGE-TO-FREQUENCY (V/F)

CIRCUIT DESCRIPTION

The TC9400 V/F converter operates on the principal

of charge balancing. The operation of the TC9400 is easily

current is then converted to a charge on the integrating

capacitor and shows up as a linearly decreasing voltage at

the output of the op amp. The lower limit of the output

swing is set by the threshold detector, which causes the

reference voltage to be applied to the reference capacitor

for a time period long enough to charge the capacitor to

the reference voltage. This action reduces the charge on

amount.

VOLTAGE-TO-FREQUENCY/

FREQUENCY-TO-VOLTAGE CONVERTERS

TC9400

TC9401

TC9402