AD7706 Analog Devices, AD7706 Datasheet - Page 40

• Manufacturer Part Number: AD7706
• Description: 3V/5V, 1mW, 3-Channel Pseudo Differential, 16-Bit Sigma-Delta ADC
• Manufacturer: Analog Devices

Specifications of AD7706

• Resolution (bits): 16bit
• # Chan: 3
• Sample Rate: n/a
• Interface: Ser,SPI
• Analog Input Type: Diff-Bip,Diff-Uni
• Ain Range: Bip (Vref)/(PGA Gain),Uni (Vref)/(PGA Gain)
• Adc Architecture: Sigma-Delta
• Pkg Type: DIP,SOIC,SOP

AD7705/AD7706
SMART TRANSMITTERS
Another application where the low power, single-supply, 3-wire
interface capabilities of the AD7705/AD7706 are beneficial is in
smart transmitters. Figure 28 shows a block diagram of a smart
transmitter using the AD7705. Because a smart transmitter
must operate from a 4 to 20 mA loop, tolerances in the loop
SENSORS
RTD
mV
TC
Ω
V
DD
AD7705
GND
ISOLATED GROUND
REF IN
ISOLATED SUPPLY
MCLK OUT
MCLK IN
4.7μF
100kΩ
ISOLATION
Figure 28. Smart Transmitter Using the AD7705
BARRIER
Rev. C | Page 40 of 44
MICROCONTROLLER UNIT
•PID
•RANGE SETTING
•CALIBRATION
•LINEARIZATION
•OUTPUT CONTROL
•SERIAL COMMUNICATION
•HART PROTOCOL
V
CC
COM
MAIN TRANSMITTER ASSEMBLY
mean that the current available to power the transmitter can be
as low as 3.5 mA. The AD7705 consumes only 320 μA, leaving
at least 3 mA available for the rest of the transmitter. The
AD7705, with its dual-input channel, is ideally suited for
systems requiring an auxiliary channel whose measured
variable is used to correct that of the primary channel.
4.7μF
0.01μF
V
REF OUT1
REF OUT2
REF IN
C1 C2 C3
CC
0.01μF
2.2μF
AD421
0.1μF
0.0033μF
BOOST
COMP
DRIVE
LOOP
COM
RTN
DN25D
1000pF
0.01μF
1kΩ
4mA
TO
20mA