JAJSSA8 November 2023 BQ76905
PRODUCTION DATA
The BQ76905 device supports measurement of an external thermistor on the TS pin. The device includes an internal 20-kΩ pullup resistor to bias the thermistor during measurement. The TS pin can be selected for thermistor measurement or general purpose ADCIN measurement using a data memory setting.
When the pin is selected for thermistor measurement, the internal pullup resistor is used to bias the pin during the measurement. In order to provide a high precision result, the device uses the same 1.8 V internal 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. Because the pullup resistor is only enabled during the pin measurement, it is recommended to limit the capacitance at this node to reduce the effect of incomplete settling when the pullup resistor is biased. The capacitance is recommended to stay below 4 nF when in highest resolution mode, or 500 pF when in highest speed mode.
If the pin is selected for general purpose ADCIN measurement, the pullup resistor is not enabled during measurement, and the ADC uses VREF1 for its reference when measuring the pin.
The data is reported in units of 16-bit ADC counts. The fullscale digital value reflects an analog input level of its reference × 5 / 3. So when the TS pin is measuring a thermistor in ratiometric mode using the 1.8V internal regulator for its reference, the 16-bit LSB is 1.8 V × 5 / 3 / 32768 ≅ 91.55 μV. When the TS pin is measuring in ADCIN mode using the VREF1 reference, the 16-bit LSB is VREF1 × 5 / 3 / 32768 ≅ 61.80 μV.