More detailed specification of SAADC input impedance?

[snygaard]

I’m searching for some more detailed information of the SAADC input impedance.

Please see attached file for details and questions.

Nordic Semiconductor question 20190315.pdf

[Kenneth]

Hello,

The R_INPUT value is a question that pop up from time to time when reading the datasheet, since it does state >1Mohm as a typical value, which initially may seem very concerning. The good news though is that it is much higher, and I have still not seen anyone raise a concern after going to production or show any measurement that give any indication that the leakage current is higher than the few nA range.

The explanation behind the >1Mohm value is that there has not been any simulation on the bias/leakage current for the input, simply because it is very, very low, and it is not an issue. If you need a number for your calculations, you can safely presume that worst case you will need to bias the input pin with up to 0.1uA (but for all practical purposes it will be 10-100-1000x lower than this, even worst case I doubt it will ever go above 10nA).

Best regards,
Kenneth

[snygaard]

Thank you for an explanation of the ">1Mohm" statement.
You shall consider changing the specification in the next datasheet revision.