SAADC VDD measurement offset

RE: SAADC VDD measurement offset

Vidar Berg — Fri, 20 Dec 2019 10:45:29 GMT

Hi Vojislav,

Thank you for the update. So it appears t be hw related as you said. Maybe the supply voltage drops under load? Maybe you have done it already, but I would have tried to verify with the voltage on the input, preferably with an oscilloscope.

RE: SAADC VDD measurement offset

Vojislav — Fri, 20 Dec 2019 09:43:00 GMT

Hi Vidar,

I run the same code on the 52 DK board and got good results. I measured 2.872V on the connector P22 when the USB is powering the dev board and got results (without my offset in the calculation): 2850 to 2862 (mV). I can assume this is correct because there is an error in SAADC due to many factors.

From this, it seems that the problem is with hardware (probably internal module components).

I will investigate this furthermore.

RE: SAADC VDD measurement offset

Vojislav — Fri, 20 Dec 2019 08:53:33 GMT

Hi Vidar,

I am Otii solution for powering the project. I am quite sure it is providing the correct voltage and also I did the measurement and got 3V.

I am not using 52 DK to for testing and developing instead, I have custom board with a minimum number of components based on module ISP1507-AL (nRF52810-CAAA chipset). The power pins are directly connected to the power supply and in the picture below you can see the internal schematic of the module.

So from this, I do not see any "obstacles" that would lower the voltage before the MCU.
I will also try this on the 52 DK to be sure that it is not hardware related.

Also, low power SAADC mode is enabled.

Let me know what do you think.

Best regards,
Vojislav.

RE: SAADC VDD measurement offset

Vidar Berg — Thu, 19 Dec 2019 13:41:45 GMT

Hi,

It looks like the code is correct. Do you have a stable supply voltage when it's sampled, or is it battery-powered, and Is the 3V VDD voltage measured on the input? The 52 DK has a reverse voltage protection diode that will drop the voltage by about 300 mV.

Best regards,

Vidar