nRF52832 SAADC circuit R_INPUT value

[Farhang]

Hi there,

I am getting some error in my SAADC measurements and I believe it's due to the R_INPUT forming a parallel resistance with my voltage divider at the input (the voltage divider is meant to scale down the voltage of interest to under 2.4 Volts so it can be measured by the MCU). The values I have chosen for my divider are 1M and 68K.

I would like to know the typical value of R_INPUT so I can estimate what the equivalent resistance of my voltage divider is. The specification says R_INPUT is >1M but this doesn't help as it covers a huge range and theoretically it covers infinite resistance (open circuit).

infocenter.nordicsemi.com/index.jsp

I suspect there's a good reason for this but if not I would like to know the typical value so that I can scale my measurements accordingly.

[Jørn]

Was the PSEL switch connected or disconnected when you did your measurements? if it was connected, could you make sure it is disconnected and redo the measurements? This would reduce any possible additional sources of error.