SBAU206B april 2015 – may 2023 ADS1262 , ADS1263
The ADS1263EVM includes provisions for using a PCB-mounted thermistor to measure the cold junction of a thermocouple connected to the AIN8 and AIN9 inputs on J4. Figure 3-6 shows how top- and bottom-layer copper pours create an isothermal bridge between the AIN8 and AIN9 inputs. This bridge helps make sure that thermistor RT1 measures the same temperature as the thermocouple cold junction at inputs J4:1 and J4:2, enabling a more accurate thermocouple measurement.
As discussed in Section 3.1.2.2, thermistor RT1 is not populated by default on the ADS1263EVM. Choose a 10-kΩ NTC thermistor in a 0603 package for this component. Additionally, populate the 10-kΩ bias resistor (R34) to create a valid resistor divider as well as the 0-Ω resistor (R36) to directly bias the sensor using the 2.5-V reference output of the ADS1263. Populating the linearization resistor (R33) is optional.
Measure the thermistor voltage as described in Section 3.1.2.2. However, note that the ADS1263 is a multiplexed ADC that can only measure one single-ended or differential input per conversion cycle. As a result, the thermocouple and CJC measurements must be taken separately and then manipulated in software to determine the resulting temperature. To learn more about CJC as well as how to use this value to determine the true measured temperature, see the A Basic Guide to Thermocouple Measurements application note.