AD7714
Smart Transmitters
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.
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.
ISOLATION
BARRIER
MAIN TRANSMITTER ASSEMBLY
ISOLATED SUPPLY
3V
VOLTAGE
REGULATOR
VOLTAGE
REFERENCE
V
CC
VOLTAGE
REFERENCE
AV
DV
REF IN
DD
DD
INPUT/OUTPUT
STAGE
SENSORS
RTD
mV
ohm
D/A
CONVERTER
4–20mA
MICROCONTROLLER UNIT
SIGNAL
CONDITIONER
*PID
TC
MCLK
IN
LOOP
RTN
AD7714
*RANGE SETTING
*CALIBRATION
*LINEARIZATION
*OUTPUT CONTROL
*SERIAL COMMUNICATION
*HART PROTOCOL
COM
3V
AMBIENT
TEMP.
SENSOR
WAVEFORM
SHAPER
BANDPASS
FILTER
HART
MODEM
BELL 202
MCLK
OUT
AGND
DGND
COM
ISOLATED GROUND
Figure 16. Smart Transmitter Using the AD7714
–38–
REV. C
ADI [ ADI ]
