FUNCTIONAL BLOCK DIAGRAM

REV. A

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a

Loop-Powered 4–20 mA

Sensor Transmitter

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

Tel: 617/329-4700

Fax: 617/326-8703

AD693

FEATURES

Instrumentation Amplifier Front End

Loop-Powered Operation

Precalibrated 30 mV or 60 mV Input Spans

Independently Adjustable Output Span and Zero

Precalibrated Output Spans: 4–20 mA Unipolar

0–20 mA Unipolar

12

8 mA Bipolar

Precalibrated 100

RTD Interface

6.2 V Reference with Up to 3.5 mA of Current Available

Uncommitted Auxiliary Amp for Extra Flexibility

Optional External Pass Transistor to Reduce

Self-Heating Errors

PRODUCT DESCRIPTION

The AD693 is a monolithic signal conditioning circuit which

accepts low-level inputs from a variety of transducers to control a

standard 4–20 mA, two-wire current loop. An on-chip voltage

reference and auxiliary amplifier are provided for transducer

excitation; up to 3.5 mA of excitation current is available when the

device is operated in the loop-powered mode. Alternatively, the

device may be locally powered for three-wire applications when

0–20 mA operation is desired.

Precalibrated 30 mV and 60 mV input spans may be set by

simple pin strapping. Other spans from 1 mV to 100 mV may

be realized with the addition of external resistors. The auxiliary

amplifier may be used in combination with on-chip voltages to

provide six precalibrated ranges for 100

Ω RTDs. Output span

and zero are also determined by pin strapping to obtain the

standard ranges: 4–20mA, 12

± 8 mA and 0–20 mA.

Active laser trimming of the AD693’s thin-film resistors result

in high levels of accuracy without the need for additional

adjustments and calibration. Total unadjusted error is tested on

every device to be less than 0.5% of full scale at +25

°C, and less

than 0.75% over the industrial temperature range. Residual

nonlinearity is under 0.05%. The AD693 also allows for the use

of an external pass transistor to further reduce errors caused by

self-heating.

For transmission of low-level signals from RTDs, bridges and

pressure transducers, the AD693 offers a cost-effective signal

conditioning solution. It is recommended as a replacement for

discrete designs in a variety of applications in process control,

factory automation and system monitoring.

The AD693 is packaged in a 20-pin ceramic side-brazed DIP,

20-pin Cerdip, and 20-pin LCCC and is specified over the

–40

°C to +85°C industrial temperature range.

PRODUCT HIGHLIGHTS

1. The AD693 is a complete monolithic low-level voltage-to-

current loop signal conditioner.

2. Precalibrated output zero and span options include

4–20 mA, 0–20 mA, and 12

± 8 mA in two- and three-wire

configurations.

3. Simple resistor programming adds a continuum of ranges

to the basic 30 mV and 60 mV input spans.

4. The common-mode range of the signal amplifier input

extends from ground to near the device’s operating voltage.

5. Provision for transducer excitation includes a 6.2 V

reference output and an auxiliary amplifier which may be

configured for voltage or current output and signal

amplification.

6. The circuit configuration permits simple linearization of

bridge, RTD, and other transducer signals.

7. A monitored output is provided to drive an external pass

transistor. This feature off-loads power dissipation to

extend the temperature range of operation, enhance

reliability, and minimize self-heating errors.

8. Laser-wafer trimming results in low unadjusted errors and

affords precalibrated input and output spans.

9. Zero and span are independently adjustable and noninteractive

to accommodate transducers or user defined ranges.

10. Six precalibrated temperature ranges are available with a

100

Ω RTD via pin strapping.