why has PA4 (ADC1CH18) low impedance as soon as adc2 temp channel gets initialized

froesel · ‎2022-10-12

Hello,

In our project, we are using a STM32H7B3ZI, LQFP144 package.

We are using a simple 24v, 33k/2k7 voltage divider to sense a voltage and expected a voltage at this pin ~1.8V.

The signal is connected to PA4, evaluated by ADC1CH18, no PU, no PD.

Furthermore, we are using the temp channel of ADC2.

We use CubeMX for configuration, version 1.10.

During initialization, everything is fine, the signal has something around 1.78V. As soon as ADC2 is initialized, the PA4 pin will be pulled down to 0.7V. This is not expected behavior, as PA4 is not connected to ADC2 in any way and the input impedance should way higher than ~2k.

We can reproduce this bahaviour with serveral PCBA. Furthermore, we unsoldered the package pin,and voltage divider was fine. Same bahavior after deleting flash of uC.

Could you please explain this behavior? Are there known issues?

Thank you,

Florian

Amel NASRI · ‎2022-10-20

Internal ticket number: 137106 (This is an internal tracking number and is not accessible or usable by customers).

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