REV. C

Information furnished by Analog Devices is believed to be accurate and

reliable. However, no responsibility is assumed by Analog Devices for its

use, nor for any infringements of patents or other rights of third parties

which may result from its use. No license is granted by implication or

otherwise under any patent or patent rights of Analog Devices.

a

Integrated Circuit

Voltage-to-Frequency Converter

AD537*

PRODUCT DESCRIPTION

The AD537 is a monolithic V-F converter consisting of an input

amplifier, a precision oscillator system, an accurate internal ref-

erence generator and a high current output stage. Only a single

external RC network is required to set up any full-scale (F.S.)

frequency up to 100 kHz and any F.S. input voltage up to

±30 V. Linearity error is as low as ±0.05% for 10 kHz F.S., and

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

all temperature coefficient (excluding the effects of external

components) is typically

±30 ppm/°C. The AD537 operates

from a single supply of 5 V to 36 V and consumes only 1.2 mA

quiescent current.

A temperature-proportional output, scaled to 1.00 mV/K,

enables the circuit to be used as a reliable temperature-to-

frequency converter; in combination with the fixed reference

output of 1.00 V, offset scales such as 0

°C or 0°F can be generated.

The low drift (1

µV/°C typ) input amplifier allows operation

directly from small signals (e.g., thermocouples or strain gages)

while offering a high (250 M

Ω) input resistance. Unlike most

V–F converters, the AD537 provides a square-wave output, and

can drive up to 12 TTL loads, LEDs, very long cables, etc.

The excellent temperature characteristics and long-term stability

of the AD537 are guaranteed by the primary bandgap reference

generator and the low T.C. silicon chromium thin film resistors

used throughout.

The device is available in either a 14-lead ceramic DIP or a 10-lead

metal can; both are hermetically sealed packages.

*Protected by Patent Nos. 3,887,963 and RE 30,586.

FEATURES

Low Cost A–D Conversion

Versatile Input Amplifier

Positive or Negative Voltage Modes

Negative Current Mode

High Input Impedance, Low Drift

Single Supply, 5 V to 36 V

Linearity:

0.05% FS

Low Power: 1.2 mA Quiescent Current

Full-Scale Frequency up to 100 kHz

1.00 V Reference

Thermometer Output (1 mV/K)

F-V Applications

MIL-STD-883 Compliant Versions Available

PIN CONFIGURATIONS

D-14 Package

H-10A Package

LOGIC GND

SYNC

OUTPUT

CAP

CAP

1

2

14

13

5

6

7

10

9

8

3

4

12

11

AD537

DRIVER

CURR-

TO-FREQ

CONV

BUF

PRECISION

VOLTAGE

REFERENCE

DRIVER

CURR-

TO-FREQ

CONV

PRECISION

VOLTAGE

REFERENCE

AD537

LOGIC GND

OUTPUT

CAP

CAP

(CONNECTED TO CASE)

BUF

10

9

8

7

6

5

4

3

2

1

The AD537 is available in three performance/temperature

grades; the J and K grades are specified for operation over the

0

°C to +70°C range while the AD537S is specified for operation

over the extended temperature range, –55

°C to +125°C.

PRODUCT HIGHLIGHTS

1. The AD537 is a complete V-F converter requiring only an

external RC timing network to set the desired full-scale fre-

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

tor output stage. Any full-scale input voltage range from

accommodated by proper selection of timing resistor. The

full-scale frequency is then set by the timing capacitor from

the simple relationship, f = V/10RC.

2. The power supply requirements are minimal, only 1.2 mA

quiescent current is drawn from a single positive supply from

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

easily be connected for below ground operation.

3. F-V converters with excellent characteristic are also easy to

build by connecting the AD537 in a phase-locked loop. Ap-

plication particulars are shown in Figure 6.

4. The versatile open-collector NPN output stage can sink up

to 20 mA with a saturation voltage less than 0.4 volts. The

Logic Common terminal can be connected to any level be-

easy direct interface to any logic family with either positive or

negative logic levels.

5. The AD537 is available in versions compliant with MIL-

STD-883. Refer to the Analog Devices Military Product

Databook or current AD537/883B data sheet for detailed

specifications.

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., 2000