CN0326 Datasheet, PDF (1/7 Pages) Analog Devices – Devices Connected

Circuits from the Lab™ reference circuits are engineered and
tested for quick and easy system integration to help solve today’s
analog, mixed-signal, and RF design challenges. For more
information and/or support, visit www.analog.com/CN0326.
Circuit Note
CN-0326
Devices Connected/Referenced
AD7793
3-Channel, Low Noise, Low Power,
24-Bit Sigma Delta ADC
ADuM5401
Quad-Channel Isolators with
Integrated DC/DC Converter
AD8603
MicroPower RRIO Low Noise
Precision Single CMOS Op Amp
Isolated Low Power pH Monitor with Temperature Compensation
EVALUATION AND DESIGN SUPPORT
Circuit Evaluation Boards
CN0326 Evaluation Board (EVAL-CN0326-PMDZ)
System Demonstration Platform (EVAL-SDP-CB1Z)
SDP PMOD Interposer Board (SDP-PMD-IB1Z)
Design and Integration Files
Schematics, Layout Files, Bill of Materials
CIRCUIT FUNCTION AND BENEFITS
The circuit shown in Figure 1 is a completely isolated low power
pH sensor signal conditioner and digitizer with automatic
temperature compensation for high accuracy.
The circuit gives 0.5% accurate readings for pH values from 0 to
14 with greater than 14-bits of noise-free code resolution and is
suitable for a variety of industrial applications such as chemical,
food processing, water, and wastewater analysis.
This circuit supports a wide variety of pH sensors that have very
high internal resistance that can range from 1 MΩ to several
GΩ, and digital signal and power isolation provides immunity
to noise and transient voltages often encountered in harsh
industrial environments.
3.3V_ISO
FERRITE BEAD:
MURATA BLM21PG331SN1D
BEAD
210µA
TO
Pt1000
RTD
P1
pH SENSOR
J1
1MΩ
3.3V_ISO
AD8603
10kΩ
1µF
10kΩ
1µF
10kΩ
5kΩ
1µF
AV_DD
IOUT2
DV_DD
AIN2(+)
3.3V_ISO
V_ISO
3.3V
V_DD1
CS
AD7793
SCLK
AIN1(+)
DIN
AIN1(–)
AIN2(–)
DOUT/
RDY
RFIN(+)/AIN3(+)
RFIN(–)/AIN3(–)
GND
V_OA
V_OB
V_OC
V_ID
V_IA
V_IB
V_IC
V_OD
GND_ISO GND₁
ADUM5401
CS
SCLK
DIN
DOUT/RDY
GND_ISO
Figure 1. pH Sensor Circuit (Simplified Schematic: All Connections and Decoupling Not Shown)
Rev. 0
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