REV. B

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a

AD654

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 781/329-4700

World Wide Web Site: http://www.analog.com

Fax: 781/326-8703

© Analog Devices, Inc., 1999

Low Cost Monolithic

Voltage-to-Frequency Converter

FEATURES

Low Cost

Single or Dual Supply, 5 V to 36 V,

5 V to

18 V

Full-Scale Frequency Up to 500 kHz

Minimum Number of External Components Needed

Versatile Input Amplifier

Positive or Negative Voltage Modes

Negative Current Mode

High Input Impedance, Low Drift

Low Power: 2.0 mA Quiescent Current

Low Offset: 1 mV

PRODUCT DESCRIPTION

The AD654 is a monolithic V/F converter consisting of an input

amplifier, a precision oscillator system, and a high current output

stage. A single RC network is all that is required to set up any

full scale (FS) frequency up to 500 kHz and any FS input voltage

up to

± 30 V. Linearity error is only 0.03% for a 250 kHz FS,

and operation is guaranteed over an 80 dB dynamic range. The

overall temperature coefficient (excluding the effects of external

components) is typically

±50 ppm/°C. The AD654 operates from

a single supply of 5 V to 36 V and consumes only 2.0 mA quies-

cent current.

The low drift (4

µV/°C typ) input amplifier allows operation

directly from small signals such as thermocouples or strain gauges

while offering a high (250 M

Ω) input resistance. Unlike most

V/F converters, the AD654 provides a square-wave output, and

can drive up to 12 TTL loads, optocouplers, long cables, or

similar loads.

PRODUCT HIGHLIGHTS

1. Packaged in both an 8-lead mini-DIP and an 8-lead SOIC

package, the AD654 is a complete V/F converter requiring

only an RC timing network to set the desired full-scale fre-

quency and a selectable pull-up resistor for the open-collector

output stage. Any full scale input voltage range from 100 mV

dated by proper selection of the timing resistor. The full-

scale frequency is then set by the timing capacitor from the

simple relationship, f = V/10 RC.

2. A minimum number of low cost external components are

necessary. A single RC network is all that is required to set

up any full scale frequency up to 500 kHz and any full-scale

input voltage up to

±30 V.

3. Plastic packaging allows low cost implementation of the

standard VFC applications: A/D conversion, isolated signal

transmission, F/V conversion, phase-locked loops, and tuning

switched-capacitor filters.

4. Power supply requirements are minimal; only 2.0 mA of

quiescent current is drawn from the single positive supply

from 4.5 volts to 36 volts. In this mode, positive inputs can

can easily be connected for below ground operation.

5. The versatile open-collector output stage can sink more than

10 mA with a saturation voltage less than 0.4 volts. The Logic

Common terminal can be connected to any level between

direct interface to any logic family with either positive or

negative logic levels.

FUNCTIONAL BLOCK DIAGRAM

3

2

1

5

8

7

6

AD654

4

DRIVER

OSC

LOGIC

COMMON