Malfunction of ADC123_IN1 in Nucleo-F756ZG

[Ryosuke]

I'm in trouble with the high err rate of ADC123_IN1 in "STM32 Nucleo-144 development board with STM32F756ZG MCU".

I've purchased two of the same thing, and both of them have trouble in ADC123_IN1.

I had tried 4 channels: ADC123_IN1, ADC123_IN4, ADC123_IN8, ADC123_IN2, but only ADC123_IN1 has high err rate.

Could you tell me how to get ADC value accurately.

I attached ADC measurement results just in case. (ADC_measurement_results.PNG)

[Ryosuke]

Thank you for your response.

But in that case, I cannot understand why ADC123_IN2(PA2) worked successfully.

[SofLit · Accepted solution]

Because MDIO is bidirectional and when you you did the measure, it's not forcing the voltage of PA2 but need also to remove SB160. 

So please remove SB13 and redo the test on PA1 and tell what you found.

Apart of forcing the voltage from outside of the pin there is also the impedance that will influence the ADC impedance input.

So please remove all the connections to these pins for a good ADC conversion.