nRF52832 analog input high-Z

[Michael]

Hello,

I'm designing a project with the nRF52832 where I will use an external SPI ADC. For debug and backward compatibility purposes, I also plan to use the SAADC. The analog input will be connected to both the SPI ADC and the SAADC (in parallel). This will enable using whichever ADC in software (they will not work simultaneously - only one of them at any given time).

The external ADC's input impedance is very high (500 Megaohms) so I'm not worried it will load down the SAADC's input.

However, the SAADC's input impedance is 1 Megaohms as stated in the datasheet. This will load down the external ADC's inputs.

I want to be able to disconnect the SAADC from the circuit effectively without using 0 ohm resistors (jumpers) which take up valuable place on the board.

If I put the SAADC analog input into disconnected mode (PSELN/PSELP = 0), does that put it into high-Z mode, or is the input impedance of the analog inputs 1 Megaohms no matter what?

Thanks, Michael.

[Turbo J]

is the input impedance of the analog inputs 1 Megaohms no matter what?

I would assume that the input is 1 MOhm no matter what. Remember that the NRF52x has no dedicated analog pins, so there might be some resitual current from the GPIO part even when it is disabled.

And there is still an analog multiplexer present that switches inputs to the analog peripherials (SAADC, COMP, LPCOMP).

Those 0-R resistors are tiny in a 01005 package.