ZHCSMR2B December 2020 – December 2021 BQ76942
The BQ76942 device includes an on-chip temperature measurement and can support up to nine external thermistors on multifunction pins (TS1, TS2, TS3, CFETOFF, DFETOFF, ALERT, HDQ, DCHG, and DDSG). The device includes an internal pullup resistor to bias a thermistor during measurement.
The internal pullup resistor has two options that can set the pullup resistor to either 18-kΩ or 180-kΩ (or none at all). The 18-kΩ option is intended for use with thermistors such as the Semitec 103-AT, which has 10-kΩ resistance at room temperature. The 180-kΩ option is intended for use with higher resistance thermistors such as the Semitec 204AP-2, which has 200-kΩ resistance at room temperature. The resistor values are measured during factory production and stored within the device for use during temperature calculation. The individual pin configuration registers determine which pin is used for a thermistor measurement, what value of pullup resistor is used, as well as whether the thermistor measurement is used for a cell or FET temperature reading.
To provide a high precision temperature result, the device uses the same 1.8 V LDO voltage for the ADC reference as is used for biasing the thermistor pullup resistor, thereby implementing a ratiometric measurement that removes the error contribution from the LDO voltage level. The device processes the digitized thermistor voltage to calculate the temperature based on multiorder polynomials, which can be programmed by the user based on the specific thermistor selected.