Due to thermistors often being attached to cells and possibly needing long wires to connect back to the BQ769x2, it may be helpful to add a capacitor from the thermistor pin to the device VSS to filter the unexpected noise. However, it is important to not use too large of a value of capacitor, since this affects the settling time when the thermistor is biased and measured periodically. A general rule recommended in BQ769x2 datasheet is to keep the time constant of the circuit < 5% of the measurement time. When Settings:Configuration:Power Config[FASTADC] = 0, the measurement time is approximately 3ms, and with [FASTADC] = 1 the measurement time is halved to approximately 1.5ms.

To obtain temperature accuracy, the value of capacitor is recommended to be smaller based on the test results. When measuring a fix 18kΩ resistance with a 1nF filter capacitances, slow signal edges of thermistor pin voltage are observed in Figure 5-1. This results in 2mV voltage measurement error which effects the temperature measurement accuracy. Figure 5-2 shows the result of reducing capacitance to 220pF. The measured voltage is close to the value without capacitor on the pin.

Figure 5-1 Thermistor Pin Voltage with 1nF Capacitance, 18kΩ Fix Resistance

Figure 5-2 Thermistor Pin Voltage with 220pF Capacitance, 18kΩ Fix Resistance