3-294

TELCOM SEMICONDUCTOR, INC.

VOLTAGE-TO-FREQUENCY/

FREQUENCY-TO-VOLTAGE CONVERTERS

TC9400

TC9401

TC9402

The exact value is not critical and may be used to trim the

full-scale frequency (see "Input/Output Relationships"). Glass

film or air trimmer capacitors are recommended because of

their stability and low leakage. Locate as close as possible

to pins 5 and 3.

Power supplies of

±5V are recommended. For high-

accuracy requirements, 0.05% line and load regulation and

0.1

µF disc decoupling capacitors located near the pins are

recommended.

Adjustment Procedure

Figure 1 shows a circuit for trimming the zero location.

Recommended procedure for a 10kHz full-scale frequency

is as follows:

obtain a 10Hz output frequency.

obtain a 10kHz output frequency.

If adjustments are performed in this order, there should be

no interaction and they should not have to be repeated.

Figure 3.

500

400

300

200

100

0

–1

–2

–3

–4

–5

–6

–7

VREF (V)

1 kHz

100kHz

VDD = +5V

VSS = – 5V

RIN = 1MΩ

VIN = +10V

TA = +25°C

Improved Single Supply V/F Converter

Operation

A TC9400 which operates from a single 12 to 15V

variable power source is shown in Figure 5. This circuit uses

two Zener diodes to set stable biasing levels for the TC9400.

The Zener diodes also provide the reference voltage, so the

output impedance and temperature coefficient of the Zeners

will directly affect power supply rejection and temperature

performance.

Full scale adjustment is accomplished by trimming the

input current. Trimming the reference voltage is not recom-

mended for high accuracy applications unless an op amp is

used as a buffer, because the TC9400 requires a low

for more information).

The circuit of Figure 5 will directly interface with CMOS

logic operating at 12V to 15V. TTL or 5V CMOS logic can be

accommodated by connecting the output pullup resistors to

the +5V supply. An optoisolator can also be used if an

isolated output is required.