FUNCTIONAL BLOCK DIAGRAM

RGA RGB

INST

AMP

SHUT-

DOWN

GND

SENSE

DGND

SHUTDOWN

2.5V

REF

MATCHED

CURRENT

SOURCES

NULLA

NULLB

ADT70

PIN CONFIGURATIONS

20-Lead P-DIP

(N Suffix)

SHUTDOWN

14

13

12

11

17

16

15

20

19

18

10

9

8

1

2

3

4

7

6

5

AGND

BIAS

DGND

NULLA

NULLB

RGA

RGB

GND SENSE

a

ADT70

TOP VIEW

(Not to Scale)

20-Lead SOIC

(R Suffix)

14

13

12

11

17

16

15

20

19

18

10

9

8

1

2

3

4

7

6

5

AGND

BIAS

DGND

SHUTDOWN

NULLA

NULLB

RGA

RGB

GND SENSE

ADT70

TOP VIEW

(Not to Scale)

a

REV. 0

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

PRTD Conditioning Circuit

and Temperature Controller

ADT70*

FEATURES

PRTD Temperature Measurement Range

Typical IC Measurement Error

1 C

Includes Two Matched Current Sources

Rail-to-Rail Output Instrumentation Amp

Uncommitted, Rail-to-Rail Output Op Amp

On-Board

2.5 V Reference

Temperature Coefficient

25 ppm/ C

5 V or

5 V Operation

Supply Current 4 mA Max

10

A Max in Shutdown

APPLICATIONS

Temperature Controllers

Portable Instrumentation

Temperature Acquisition Cards

GENERAL DESCRIPTION

The ADT70 provides excitation and signal conditioning for

resistance-temperature devices (RTDs). It is ideally suited for

1 k

Ω Platinum RTDs (PRTDs), allowing a very wide range of

temperature measurement. It can also easily interface to 100

Ω

PRTDs. Using a remote, low cost thin-film PRTD, the ADT70

can measure temperature in the range of –50

°C to +500°C.

With high performance platinum elements, the temperature

change can be extended to 1000

°C. Accuracy of the ADT70

and PRTD system over a –200

°C to +1000°C temperature

range heavily depends on the quality of the PRTD. Typically

the ADT70 will introduce an error of only

±1°C over the

transducer's temperature range, and the error may be trimmed

to zero at a single calibration point.

The ADT70 consists of two matched 1 mA (nominal) current

sources for transducer and reference resistor excitation, a preci-

sion rail-to-rail output instrumentation amplifier, a 2.5 V refer-

ence and an uncommitted rail-to-rail output op amp. The

ADT70 includes a shutdown function for battery powered

equipment, which reduces the quiescent current from 4 mA to

less than 10

µA. The ADT70 operates from either single +5 V

or

±5 V supplies. Gain or full-scale range for the PRTD and

ADT70 system is set by a precision external resistor connected

to the instrumentation amplifier. The uncommitted op amp may

be used for scaling the internal voltage reference, providing a

“PRTD open” signal or “over-temperature” warning, a heater

switching signal, or other external conditioning determined by

the user.

The ADT70 is specified for operation from

40

°C to 125°C

and is available in 20-lead DIP and SO packages.

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., 1998