nRF52840 input pin voltage ripple issue.

[Munkhdelger]

Hello.

I am developing device using nRF52840 and i have question about input voltage.

Circuit is converting remaining voltage of battery using  nRF52840 (Pin P0.02 AIN0 analog input) anolog to digital.

battery voltage is = 4.2V to 2.4V

nRF52840 power voltage = 3.3V

but, input voltage of nRF52840 (Pin P0.02 AIN0 analog input) is falling down(ripple) frequiently and

I dont understand what makes this falldowns(ripple).
Is there any reason this occur to nRF52840?

(this won't occur when nRF52840 power off state.)

I attached the circuit drawn and wave when ripple happens below.

Thank you!

                          

[JONATHAN LL]

Hi,

Looks like it is periodically happening every 15-16us fromt he scope that you shared. 

Do you have anything that has that interval, how often do you sample? or is there something else in you code that might match with that time periode?



Also we do recommend to have a smal cap at the pin for battery measurements, as it will draw som current:
https://devzone.nordicsemi.com/nordic/nordic-blog/b/blog/posts/measuring-lithium-battery-voltage-with-nrf52 

10nF might do the trick as well. So can test with that and see if the issue disappears. 

Regards,
Jonathan