Circuit Note

CN-0287

Circuits from the Lab® reference designs are engineered and

tested for quick and easysystemintegrationto helpsolve today’s

analog, mixed-signal, and RF design challenges. For more

informationand/orsupport, visitwww.analog.com/CN0287.

Devices Connected/Referenced

AD7193

4-Channel, 4.8 kHz, Ultralow Noise,

24-Bit Sigma-Delta ADC with PGA

ADT7310

±0.5°C Accurate, 16-Bit Digital SPI

Temperature Sensor

AD8603

Precision Micropower, Low Noise

CMOS R-to-R Input/Output

Operational Amplifiers

ADR3440

4.096 V, Micropower High Accuracy

Voltage Reference

ADG738

CMOS, Low Voltage, 3-Wire Serially-

Controlled, Matrix Switch

ADG702

CMOS Low Voltage 2 Ω SPST Switch

AD5201

33-Position Digital Potentiometer

ADuM1280

3 kV RMS Dual Channel Digital

Isolators

ADuM5401

Quad-Channel, 2.5 kV Isolators with

Integrated DC-to-DC Converter

Isolated 4-Channel, Thermocouple/RTD Temperature Measurement

System with 0.5°C Accuracy

Rev. C

CircuitsfromtheLab®referencedesignsfromAnalogDeviceshavebeendesignedandbuiltbyAnalog

Devices engineers. Standard engineering practices have been employed in the design and

constructionofeachcircuit,andtheirfunctionandperformancehavebeentestedandverifiedinalab

environment at room temperature. However, you are solely responsible for testing the circuit and

determiningitssuitabilityandapplicabilityforyouruseandapplication.Accordingly,innoeventshall

AnalogDevicesbeliablefordirect,indirect,special,incidental,consequentialorpunitivedamagesdue

toanycausewhatsoeverconnectedtotheuseofanyCircuitsfromtheLabcircuits. (Continuedonlastpage)

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EVALUATION AND DESIGN SUPPORT

Circuit Evaluation Boards

CN-0287 Circuit Evaluation Board (EVAL-CN0287-SDPZ)

System Demonstration Platform (EVAL-SDP-CB1Z)

Design and Integration Files

Schematics, Layout Files, Bill of Materials

CIRCUIT FUNCTION AND BENEFITS

The circuit shown in Figure 1 is a completely isolated 4-channel

temperature measurement circuit optimized for performance,

input flexibility, robustness, and low cost. It supports all types of

thermocouples with cold junction compensation and any type

of RTD (resistance temperature detector) with resistances up to

4 kΩ for 2-, 3-, or 4-wire connection configurations.

The RTD excitation current are is programmable for optimum

noise and linearity performance.

RTD measurements achieve 0.1°C accuracy (typical), and

Type-K thermocouple measurements achieve 0.05°C typical

accuracy because of the 16-bit ADT7310 digital temperature

sensor used for cold-junction compensation. The circuit uses a

four-channel AD7193 24-bit sigma-delta ADC with on-chip

PGA for high accuracy and low noise.

Input transient and overvoltage protection are provided by low

leakage transient voltage supressors (TVS) and Schottky diodes.

The SPI-compatible digital inputs and outputs are isolated

(2500 V rms), and the circuit is operated on a fully isolated

power supply.