oscillation at the embed analog front end circuits of SAADC in nRF52832

[Kiyoshi Iwai]

Hello,

I found the strange phenomena on nRF52832.

By using the SAADC, I have some noise on ADC Data only at a certain temperature range.

Temperature range is depend on individual IC.

I might be the circuit oscillation at analog front end of SAADC, I think.

(internal reference voltage or op amp etc,)

I tried to switch DCDC on/off, but there's no difference on phenomena.

Anyone can resolve it?

I attach the files of real data and measurement condition.

Best regards,

Kiyoshi Iwai

3426.SAADC_noise_devzone.zip

[Kiyoshi Iwai]

Hello Kenneth,

Thanks for reply.

I have confirmed the status of all input pins perfectly and also added 1.5ms delay .

But this issue still occured.

Could you tell me the procedure to always use the 32kHz external crystal not to calibrate the internal RC by softdevice?

By the way, the member of Avnet has succeeded to reproduce this issue by using the nRF52 Development Kit board. Of course he used the softdevice.

What is the difference to effect on ADC transaction with softdevice or without softdevice?

Only caribration of internal RC? Anything else?

I still doubt of the oscillation of analog front end circuits and , the root cause of this issue does not concern the clock because the accuracy of the general SAADC is not so much affected by clock source, I think.

How do you think about it?

Please let me know if you have good information.

Best regards,

Kiyoshi Iwai