Strange ADC issue in STM32G491

[macbum]

Hi,

I have a very strange ADC issue which I am unable to find the root cause to. The symptom is as follows;

While performing ADC readings to ADC1 IN1 and ADC2 IN1 consecutively, the readings sometimes differ by more than 32 ADC counts. I perform this check as part of BIST. This only happens when at the same time a UART signal is coming in to USART3_RX (115kbps). To prove that the USART3_RX is causing the problem, I sever the connection or stop transmission (both produce the same result). The issue goes away and everything works fine.

What could be the issue? Is there something else I could do to mitigate this issue besides stopping the UART signal?

I have not been able to mitigate the issue so far. All my efforts so far to uncover the issue have not yielded any results.

I am aware that these 2 channels are essentially routed to the same pin and shared by the 2 ADCs so the readings should be identical if not very close.

[AScha.3]

Hi,

>The pins are still configured as analog. This should not have any bearing on this issue. Correct?

No.

The question is also : the incoming signal on RX pin (even when cpu is "off" , analog, signal here is same).

So try 1 kohm in series at this pin. + maybe the coupling from incoming rx -> adc/opamp voltage is happening in the opamp buffer, so also try 1k series "damper" where the rx signal enters this board.