MCU upgraded from STM32F103 to STM32L475. Facing issue in ADC part. In the F103 MCU ADC clock derived from HCLK and to meet the same sampling time we used ADC clock PLLSAI1 in L475.

[Harish1]

The issue is that at the normal conditions we are able to read the ADC values properly and when we put our device in the field then we are facing noise issues in ADC values. When we put old MCU no noise issue is coming but when we put new MCU then noise issue is coming. Grounding and everything are the same for both MCU devices.

Why we are getting noise on ADC pins we are not getting? Any comments on it?

Does the clock selection make any difference?

Is the ADC in the new MCU is sensitive compare to the old MCU's?

New MCU: STM32L475

Old MCU: STM32F103

[Uwe Bonnes]

Noise is a complex subject. Carefully recheck" Grounding and everything are the same for both MCU devices" I suspect there are subtile differences. Check also sampling time of the ADC

[Harish1]

I checked already sampling time and it is the same for both.

Yes, I agree noise is a complex subject and grounding is the same for both. The only difference is F103 lies in coated PCB and L475 is uncoated.

[TDK]

The L475 has a slightly higher total unadjusted error per the datasheet, but it's unclear if this is due to higher sampling frequency.

How much noise are you seeing and what is your sample time?

Faster clocks will have more noise in general.

There's no magical solution here.

https://www.st.com/resource/en/application_note/cd00211314-how-to-get-the-best-adc-accuracy-in-stm32-microcontrollers-stmicroelectronics.pdf

[Harish1]

I am using sampling time 2.5 ADC clock cycles and ADC clock configured as 20MHz. So, the sampling time is 125ns. I believe 20MHz is not a highier value.

I have already found the application you suggested and I am going through it.