I'm developing an application using the NRF52840. I'm using the ADC, and there may be times where the signal to be measured is up to 1.8V, but the NRF52840 is not yet powered (i.e. VDD = 0). One option I am considering is to put a resistor in series with the ADC input to limit the current through the protection diodes (see the diagram below). What current can I safely expect the protection diodes to sink when V_I/O = VDD + 0.3?
Alternatively, can you suggest an alternative approach that will not affect a high-impedance (~100 kOhm) signal when the NRF52840 is powered?
I recognize this question is similar to Protection diodes on NRF52832: max current, nRF52832 Maximum GPIO Input Voltage and Body Diode Clamping Current, but none of them have provided an an alternative to the series resistor, or recommended a safe value for that series resistor. The ESD ratings in the "Absolute maximum ratings" table do not seem to be relevant as those reflect a single high-voltage pulse rather than a constant low level.
