AD693

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FEATURES

Instrumentation Amplifier Front EndLoop-Powered Operation

Precalibrated 30mV or 60mV Input Spans

Independently Adjustable Output Span and ZeroPrecalibrated Output Spans:4–20 mA Unipolar

0–20 mA Unipolar12 8mA Bipolar

Precalibrated 100 RTD Interface

6.2 V Reference with Up to 3.5 mA of Current AvailableUncommitted Auxiliary Amp for Extra FlexibilityOptional External Pass Transistor to ReduceSelf-Heating Errors

PRODUCT DESCRIPTIONThe AD693 is a monolithic signal conditioning circuit whichaccepts low-level inputs from a variety of transducers to control astandard 4–20mA, two-wire current loop. An on-chip voltagereference and auxiliary amplifier are provided for transducer

excitation; up to 3.5mA of excitation current is available when thedevice is operated in the loop-powered mode. Alternatively, thedevice may be locally powered for three-wire applications when0–20mA operation is desired.

Precalibrated 30 mV and 60 mV input spans may be set bysimple pin strapping. Other spans from 1 mV to 100 mV maybe realized with the addition of external resistors. The auxiliaryamplifier may be used in combination with on-chip voltages toprovide six precalibrated ranges for 100 RTDs. Output spanand zero are also determined by pin strapping to obtain thestandard ranges: 4–20mA, 12 ± 8 mA and 0–20 mA.

Active laser trimming of the AD693’s thin-film resistors resultin high levels of accuracy without the need for additional

adjustments and calibration. Total unadjusted error is tested onevery device to be less than 0.5% of full scale at +25°C, and lessthan 0.75% over the industrial temperature range. Residualnonlinearity is under 0.05%. The AD693 also allows for the useof an external pass transistor to further reduce errors caused byself-heating.

For transmission of low-level signals from RTDs, bridges andpressure transducers, the AD693 offers a cost-effective signalconditioning solution. It is recommended as a replacement fordiscrete 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.REV.A

Information furnished by Analog Devices is believed to be accurate andreliable. However, no responsibility is assumed by Analog Devices for itsuse, nor for any infringements of patents or other rights of third partieswhich may result from its use. No license is granted by implication orotherwise under any patent or patent rights of Analog Devices.

Loop-Powered 4–20 mA

Sensor Transmitter

AD693

FUNCTIONAL BLOCK DIAGRAM

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-wireconfigurations.3.Simple resistor programming adds a continuum of rangesto 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 beconfigured for voltage or current output and signalamplification.6.The circuit configuration permits simple linearization ofbridge, RTD, and other transducer signals.7.A monitored output is provided to drive an external passtransistor. This feature off-loads power dissipation toextend the temperature range of operation, enhancereliability, and minimize self-heating errors.8.Laser-wafer trimming results in low unadjusted errors andaffords precalibrated input and output spans.9.Zero and span are independently adjustable and noninteractiveto accommodate transducers or user defined ranges.10.Six precalibrated temperature ranges are available with a

100 RTD via pin strapping.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.Tel: 617/329-4700Fax: 617/326-8703

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