10.6 Thermistor Temperature Measurement
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 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.
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Figure 10-3. External Thermistor Biasing
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 the user can be program, based on
the specific thermistor selected.
10.7 Factory Trim of Voltage ADC
The BQ769142 device includes factory trim for the cell voltage ADC measurements to optimize the voltage
measurement performance even if the customer does no further calibration. The customer can perform
calibration on the production line to further optimize the performance in the system. The trim information is used
to correct the raw ADC readings before they are reported as 16-bit voltage values. The 32-bit ADC voltage data,
which is generated in units of ADC counts, is modified before reporting by subtracting a stored offset trim value.
The resulting reported data does not include any further correction (such as for gain), therefore the customer will
need to process them before use.
SLUSE91A – SEPTEMBER 2020 – REVISED FEBRUARY 2021
Copyright © 2021 Texas Instruments Incorporated
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