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

[Kenneth]

Hi Kiyoshi,

Thank you for all the measurements and your patience on this case.

I have talked to the designers, and we kindly ask you to do one more measurement. The designers believe the root cause may be noise from the internal reference voltage (0.6V). Can you kindly repeat the measurements using VDD as reference? 

I have made this case private now, so we can share confidential information if needed between us and Avnet.

Best regards,
Kenneth

 

[Kiyoshi Iwai]

Hello Kenneth,

I checked this again by using VDD/4 as reference, but this issue still occurred.

Do you have next counter measure?

And why does not your designer check the analog circuits (amp, LDO, etc.,)?

I think the root cause of this issue is not software but hardware.

So I strongly recommend to check the internal circuits operation by hardware designer himself.

By the way, Avnet says they can not see this communication because of private mode.

Could you disclose this to Avnet too?

 

Best regards,

kiyoshi Iwai

[Kenneth]

Hi Kiyoshi,

For our FAE and Avnet to get access to your cases, you need to update your profile and add Japan as Location. Can you try that?

I have reported your results and questions to our analog designers, and hope to get a reply within 1-2days. Sorry for the delay.

Best regards,
Kenneth

 

[Kiyoshi Iwai]

Hello Kenneth,

How is going the situation?

I'm waiting for good information.

Thanks,

Kiyoshi Iwai