One (BQ76920), two (BQ76930), or three (BQ76940) 10-kΩ NTC 103AT thermistors may be measured by the device. These are measured by applying a factory-trimmed internal 10-k pull-up resistance to an internal regulator value of nominally 3.3 V, the result of which can be read out from the TSx (TS1, TS2, TS3) registers.

To select thermistor measurement mode, set [TEMP_SEL] = 1.

Thermistor TS1 is connected between TS1 and VSS; TS2 is connected between TS2 and VC5x (BQ76930 and BQ76940 only); and TS3 is connected between TS3 and VC10x (BQ76940 only). These thermistors may be placed in various areas in the battery pack to measure such things as localized cell temperature, FET heating, and so forth.

The thermistor impedance may be calculated using the 14-bit ADC reading in the TS1, TS2, and TS3 registers and 10-k internal pull-up resistance as follows:

The following equations show how to use the 14-bit ADC readings in TS1, TS2, and TS3 to determine the resistance of the external 103AT thermistor:

To convert the thermistor resistance into temperature, please refer to the thermistor component manufacturer’s data sheet.