AD7714YR datasheet(38/40 Pages) AD

38 / 40 page

AD7714

REV. C

–38–

Smart Transmitters

Another area where the low power, single supply, three-wire

interface capabilities is of benefit is in smart transmitters. Here,

the entire smart transmitter must operate from the 4 mA to

20 mA loop. Tolerances in the loop mean that the amount of

current available to power the transmitter is as low as 3.5 mA.

The AD7714 consumes only 500

µA, leaving 3 mA available for

the rest of the transmitter. Figure 16 shows a block diagram of a

smart transmitter which includes the AD7714. Not shown in

Figure 16 is the isolated power source required to power the

front end.

INPUT/OUTPUT

STAGE

SIGNAL

CONDITIONER

VOLTAGE

REFERENCE

MCLK

OUT

AD7714

ISOLATED SUPPLY

ISOLATION

BARRIER

SENSORS

RTD

ohm

LOOP

RTN

MCLK

COM

4–20mA

DVDD

AMBIENT

TEMP.

SENSOR

AVDD

REF IN

AGND

DGND

ISOLATED GROUND

COM

VCC

VOLTAGE

REGULATOR

MAIN TRANSMITTER ASSEMBLY

BANDPASS

FILTER

D/A

CONVERTER

WAVEFORM

SHAPER

HART

MODEM

BELL 202

MICROCONTROLLER UNIT

*PID

*RANGE SETTING

*CALIBRATION

*LINEARIZATION

*OUTPUT CONTROL

*SERIAL COMMUNICATION

*HART PROTOCOL

VOLTAGE

REFERENCE

Figure 16. Smart Transmitter Using the AD7714

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