SBAU206B april   2015  – may 2023 ADS1262 , ADS1263

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1EVM Overview
    1. 1.1 ADS1263EVM Kit
    2. 1.2 ADS1263EVM Board
  5. 2Getting Started With the ADS1263EVM
  6. 3Analog Interface
    1. 3.1 Analog Input Options
      1. 3.1.1 ADS1263 Integrated Input Functions
        1. 3.1.1.1 ADC Inputs
        2. 3.1.1.2 IDAC Output
        3. 3.1.1.3 VBIAS Output
        4. 3.1.1.4 External Reference
        5. 3.1.1.5 Test DAC Output
        6. 3.1.1.6 GPIO
      2. 3.1.2 Analog Sensor Connections
        1. 3.1.2.1 Connecting a Thermocouple to J4 on the ADS1263EVM
        2. 3.1.2.2 Connecting a Thermistor to J3 on the ADS1263EVM
        3. 3.1.2.3 Using Thermistor RT1 for Thermocouple Cold-Junction Compensation
        4. 3.1.2.4 Connecting an RTD to J3 on the ADS1263EVM
          1. 3.1.2.4.1 Connecting a 2-Wire RTD
          2. 3.1.2.4.2 Connecting a 3-Wire RTD
          3. 3.1.2.4.3 Connecting a 4-Wire RTD
    2. 3.2 ADC Connections and Decoupling
    3. 3.3 Clocking
    4. 3.4 Voltage Reference
  7. 4Digital Interface
  8. 5Power Supplies
  9. 6Software Installation
  10. 7EVM Operation and GUI
    1. 7.1 Connecting the EVM Hardware
    2. 7.2 EVM GUI Global Settings for ADC Control
    3. 7.3 Time Domain Display
    4. 7.4 Frequency Domain Display
    5. 7.5 Histogram Display
    6. 7.6 Using the GUI to Control ADC2
  11. 8Bill of Materials, PCB Layout, and Schematics
    1. 8.1 Bill of Materials
    2. 8.2 PCB Layout
    3. 8.3 Schematics
  12. 9Revision History

3.1.2.2 Connecting a Thermistor to J3 on the ADS1263EVM

Unlike a thermocouple, thermistors are not self-powered and require a constant voltage or current source to operate. Constant voltage is typically preferred because the thermistor impedance can vary from hundreds of ohms at low temperature to hundreds of thousands of ohms at high temperature (or vice versa for a thermistor with a negative temperature coefficient). A resistor is added in series with the thermistor to create a resistor divider that can be measured by an ADC.

Connect an external thermistor directly to the J3:7 and J3:8 pins on the J3 terminal block, which corresponds to analog inputs AIN6 and AIN7, respectively. The differential filter for this differential input pair has a cutoff frequency of 50 kHz. Additionally, each input has a common-mode filter with a cutoff frequency of 497.36 kHz. AIN6 and AIN7 are connected through the filter resistors to the respective analog inputs on the ADS1263. Figure 3-4 shows the portion of the ADS1263EVM schematic with J3 and the thermistor input structure.

GUID-20221111-SS0I-KCZ8-CBHD-N7DSN6JPRGGB-low.svg Figure 3-4 ADS1263EVM Thermistor Input Structure

Figure 3-4 shows four DNP components: a thermistor (RT1), a 10-kΩ linearization resistor (R33), a 10-kΩ bias resistor (R34), and a 0-Ω bias resistor (R36) connecting REFOUT to AIN6 to bias the sensor. Resistor R33 helps linearize the thermistor output voltage over a smaller temperature range. See section 2.8.2 in the A Basic Guide to Thermocouple Measurements application note to learn more about the benefits of using a linearization resistor when measuring a thermistor. Resistor R34 was chosen to be 10-kΩ because 10 kΩ is a commonly used nominal thermistor impedance. Choosing both resistors to have the same nominal impedance balances the resistor divider at 25°C.

As stated earlier in this section, thermistors are not self-powered and require a bias source to operate. The ADS1263EVM includes two methods to bias a thermistor using the 2.5-V reference output of the ADS1263. The first option requires populating the 0-Ω resistor (R36) in Figure 3-4. The second option requires installing an external jumper wire, as shown in Figure 3-5. In either case, make sure that the reference output (REFOUT) used to bias the resistor is selected as the reference source for the ADC measurements.

GUID-20221111-SS0I-DGK2-WH4G-HSSLQ80M3WXR-low.svg Figure 3-5 Using REFOUT (input J5:2) to Bias a Thermistor