ADC measurements varying between boards of same type nRF5340

RE: ADC measurements varying between boards of same type nRF5340

Kazi Afroza Sultana — Wed, 31 Aug 2022 21:38:54 GMT

Hello,

Good to know that your problem has solved. Have you found the difference in config file comparing these Zephyr ADC API and NRFX as problem solved for NRFX?

What was your input voltage to this pin (P0.04/AIN0) ? According to component values on the provided schematic , it is 2.16V. If the value is 2.16V then it is within range.

Thanks.

Best Regards,

Kazi Afroza Sultana

RE: ADC measurements varying between boards of same type nRF5340

who9vy — Wed, 31 Aug 2022 09:50:18 GMT

Ok, I found the answer to my problem. After I flashed a minimal Zephyr ADC example I got the same results. But changing from the Zephyr ADC API to the NRFX driver the problems are gone!

So, I assume that either I'm using the Zephyr ADC API in a wrong way or there is a bug somewhere in Zephyr.

RE: ADC measurements varying between boards of same type nRF5340

hmolesworth — Tue, 30 Aug 2022 16:29:52 GMT

Regrettably it is the hardware circuit which will not work as intended. Multiple issues, mostly related to impedance. The input resistance is only loosely defined and varies between parts; at 1M+ it is of the order of the potential divider lower resistance. A second issue is phantom power into the pin when battery is connected but VCC has not yet risen, discussed on this forum recently. The solution is usually an external FET or Ideal Diode or Flying Capacitor. I only have 52832 data to hand, but believe 5340 is similar - just checked v1.2 and yes same figures for input resistance

See protection-diodes-on-nrf52840-clamping-current