S08DZ60 A/D fluctuating

[jiaqihe]

   I am using the S08DZ60 for graduation design, but I have a problem. The A/D sample value is always fluctuating,  the amplitude is about 10, and the voltage of the oscilloscope observation sampling point is stable. I tried all the methods I could think of, but it didn't work. I hope I can get any help, thank you very much. I will be very grateful if someone can help me. I really have no idea.

[tonyp]

You could average multiple readings (say, 4) per sample to minimize the fluctuation.

And use the lowest clock for the A/D.

[jiaqihe]

I have averaged multiple readings, but it works not well. Then I change the A/D clock to 1MHz, but it doesn't work. Is the problem probably in the program?

[vicentegomez]

I just read you have an error of 10 of 4096 (12 bit) ? 

Can you check if you have other modules enable at the same time that you are making the measurements? or if you have noise on the system, maybe you have a signal input in other pin that is affecting your ADC measurement 

Regards

[jiaqihe · Accepted solution]

Thank you a lot. The problem is solved, my 5V reference voltage design is problematic, causing interference to A/D sampling. Redesigned and solved.

[vicentegomez]

Excellent that you found the problem, let me know if you have more questions

[tonyp]

Is that 10 out of 1023 (10 bit mode)?

[jiaqihe]

12 bit mode, and A/D sampling reference voltage is also stable. I have changed another MCU, but it didn't work.

[vicentegomez]

Hi

Are you using high-speed mode?

We recommend to use low power configuration (ADLPC).

Regards

[jiaqihe]

I confirmed that I am using low power mode. And it didn't work.