TC9402EJD Ver la hoja de datos (PDF) - TelCom Semiconductor Inc => Microchip

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componentes Descripción

Fabricante

TC9402EJD

VOLTAGE-TO-FREQUENCY/FREQUENCY-TO-VOLTAGE CONVERTERS

TelCom Semiconductor Inc => Microchip 

VOLTAGE-TO-FREQUENCY/

FREQUENCY-TO-VOLTAGE CONVERTERS

1

TC9400

TC9401

TC9402

THRESHOLD

11 DETECT

+5V

14

VDD

THRESHOLD

DETECTOR

3µsec

DELAY

–3V

12 AMP OUT

SELF-

START

+5V

fOUT 8

RL

10kΩ

+5V

fOUT/2 10

RL

10kΩ

÷2

9

OUTPUT

COMMON

5 VREF OUT

INPUT

VIN

CINT

820pF

RIN

1MΩ

CREF

180pF

12pF

3 IIN

0V –10V

50kΩ

+5V

510kΩ

ZERO

2 ADJUST

–5V

OFFSET

ADJUST

10kΩ

20kΩ

60pF

–

OpAmp

+

IBIAS

1

RBIAS

100kΩ

TC9400

TC9401

TC9402

VSS

4

VREF

7

GND

6

REFERENCE

VOLTAGE

(TYPICALLY –5V)

–5V

Figure 1. 10 Hz to 10 kHz V/F Converter

2

3

4

5

6

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

understood by referring to Figure 1. The input voltage (VIN)

is converted to a current (IIN) by the input resistor. This

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

the integrating capacitor by a fixed amount (q = CREF ×

VREF), causing the op amp output to step up a finite

amount.

TELCOM SEMICONDUCTOR, INC.

At the end of the charging period, CREF is shorted out.

This dissipates the charge stored on the reference capaci-

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

7 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

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

must simply be long enough for full charge transfer to take

place.

3-291

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