When an adaptor is not present on the BQ21040, the IC is operating in battery only mode. During this mode of operation, there is no 50-uA current being supplied at TS and therefore essentially 0 voltage drop occurs across the NTC thermistor. Without this voltage drop, the method used to obtain temperature measurements with an adapter present as described above cannot be used. Instead, an external MCU will be used to bias 50uA of current across the thermistor. Voltage will then be measured by the MCU in the same manner that the BQ21040 does when an adapter is connected.