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[FAQ] BQ76952: How to configure a multipurpose pin to work as a thermistor in the BQ769x2 family devices?

Part Number: BQ76952
Other Parts Discussed in Thread: BQ769142, BQ76942, BQSTUDIO

How to configure a multipurpose pin to work as a thermistor in the BQ769x2 (BQ76952, BQ76942, BQ769142) family devices?

  • The BQ769x2 device family includes an on-chip temperature measurement and can also support up to nine external thermistors on multifunction pins (TS1, TS2, TS3, CFETOFF, DFETOFF, ALERT, HDQ, DCHG, and DDSG). More details can be found in the Technical Reference Manual (TRM) Section 4.8 Thermistor Temperature Measurement.

    Hardware considerations:

    As shown in Figure-2, it is recommended to place a capacitor in parallel to the thermistor when long wire connections are needed. Care must be taken when selecting the capacitor value. Choosing too large of a capacitor value can affect the settling time; resulting in inaccurate measurements. A typical capacitor value is 470pF. For a more detailed explanation in Section 16.2 Typical Applications of the Technical Reference Manual (TRM).

    Figure-1: Typical thermistor connection

    Figure-2: Thermistor with capacitor

    Multipurpose Pin Configuration:   

    Any of the nine multipurpose pins (TS1, TS2, TS3, CFETOFF, DFETOFF, ALERT, HDQ, DCHG, and DDSG) can be configured by setting DFETOFF Pin Config register shown in Figure-3.

    As an example, Figure-3 shows how to configure the DFETOFF pin as a thermistor; using the 18k Temperature without protections (it will purely report the temperature measurement).

       Figure-3 DFETOFF Pin Configurations

    Figure-4: DFETOFF pin Configured as Thermistor without protections

    Figure-5 and Figure- 6 show the readings before and after of the DFETOFF pin. This is shown in the register of BQStudio. Notice how DFETOFF displays -273.2 °C when the thermistor is not configured.

    Figure-5 shows the default temperature before configuring DFETOFF as a thermistor.

    Figure-5: Before Configurations


    Figure-6 shows the DFETOFF working as a thermistor.

    Figure-6: After Configurations

    For more details on configuring different temperature models, reference to How to configure the temperature model of BQ769x2 using the thermistor coefficient calculator tool?

    Link to BQ769x2 FAQ homepage