Hi,
We're using nRF9160 ADC to measure the battery voltage. The battery voltage is divided down with a resistor divider as seems to be the case in many other designs and examples too. Now, our battery will consist of two serial Lithium Ion cells resulting the maximum voltage to be ca 8.4V. In the initial prototypes the ADC is configured like this
In the same time, in the HW the VDD_GPIO supply is 3.3V. The battery voltage divider resistances are 6k8/4k7 which means that the maximum voltage at nRF IO can be as high as 3.43V which exceeds the VDD_GPIO voltage. Hence I see there's a conflict here, and the ADC wont be able to measure the highest battery voltages correctly.
I believe that to get the highest voltages measured correctly we need to scale down the battery voltage to be always lower than 3.3V. But what will happen if we keep the circuit like it's now? In the first protos the ADC still seems to give somewhat reasonable, but perhaps not exactly correct results even the input does exceed 3.3V. Will there eventually be something breaking down or will there just be some current leakage through protection diodes ?
Regards,
Jyrki
