Datasheet

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
mV
ohm
TC
LOOP
RTN
MCLK
IN
COM
3V
4–20mA
DV
DD
AMBIENT
TEMP.
SENSOR
AV
DD
REF IN
AGND
DGND
ISOLATED GROUND
COM
V
CC
3V
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