The input range of the SAADC is not as expected.

[TML_YT]

Hellow

We are in trouble. Please tell me what to do.

The input range of the SAADC is not as expected.

I use:
・nrf52840
・VDD=3.3V by Regulator
・nRF5_SDK_17.1.0
・Sample program Unmodified　\examples\peripheral\saadc

Therefore:
・gain=1/6
・Resolution=10bit
・Reference internal =0.6V
-->The Voltage input range should be 3.6v.

Situation & The problem
Vin=1.0V->0x011e (ok)
Vin=1.5V->0x01ab (ok)
Vin=2.0V->0x0239 (ok)
Vin=2.2V->0x024f (NG)
Vin=2.3V->0x01e1(NG)
Vin=2.4V->0x017e(NG)

If the input voltage exceeds about 2.2V, the output code is not as
expected, and if the input voltage is higher than that, the output code
value becomes smaller.

What are the causes and what can be done about it?

Please help me.

[haakonsh]

1. The UICR->REGOUT0 register was likely set to 5(3.3V) at some point, then an nrfjprog eraseall command reset the UICR->REGOUT0 to its default state, 7 (1.8V). 
   
   
2. You check for the state of the DCDC regulators, If false it means that they are operating in LDO mode. 

I hope this clears things up. Most likely Raytac ships their dk's with UICR->REGOUT0 set to 5, we do the same for our nRF52840 dongles. 

[TML_YT]

Thank you for your reply.

I asked Raytac and they said the evaluation board is working with VDDH. And I understood that it is working with LDO, not DC/DC.

I think the trouble is that Raytac shipped with UICR-> REGOUT0=5, but I did an All Erase and it went back to REGOUT0=7.
I think this is why, since All Erase, the board has a GPIO output H level of 1.8V and the SAADC input range is no longer as expected.

Finally, I have cleared things up.
Thank you for all your help and advice.

[haakonsh]

I'm Glad I could be of assitance :)