SLUUCF2C January 2021 – May 2022 BQ769142
The BQ769142 device 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). The device includes an internal pullup resistor to bias a thermistor during measurement.
The internal pull-up resistor has two options which can set the pull-up 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 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 pull-up resistor is used, as well as whether the thermistor measurement is used for a cell or FET temperature reading. For more detail on these pin configuration registers, see Section 7.4.
Command Address | Name | Comment |
---|---|---|
0x68 | Int Temperature | Internal die temperature |
0x6A | CFETOFF Temperature | CFETOFF pin thermistor |
0x6C | DFETOFF Temperature | DFETOFF pin thermistor |
0x6E | ALERT Temperature | ALERT pin thermistor |
0x70 | TS1 Temperature | TS1 pin thermistor |
0x72 | TS2 Temperature | TS2 pin thermistor |
0x74 | TS3 Temperature | TS3 pin thermistor |
0x76 | HDQ Temperature | HDQ pin thermistor |
0x78 | DCHG Temperature | DCHG pin thermistor |
0x7A | DDSG Temperature | DDSG pin thermistor |
The calculation of temperature from the measured ADC value is performed using a temperature model, which includes gain, offset, and a polynomial computation. The device includes configuration registers for one temperature model based on the 18-kΩ pull-up resistor in Calibration:18K Temperature Model, and a second temperature model based on the 180-kΩ pull-up resistor in Calibration:180K Temperature Model. This allows one type of thermistor to be used for measuring cell temperature, versus another type may be used for measuring FET temperature. The default parameters for the models match the Semitec 103-AT and 204AP-2 thermistors.
In order 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.