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STM32F303 GPIO configured as Push pull affecting ADC readings

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WillHuang:
Hi,
I'm using a STM32F303 (landing page: http://www.st.com/en/microcontrollers/stm32f303k8.html) for one of my project. I have PA0 configured as a GPIO output with push pull used to turn ON/OFF a BJT. I also have PA3 configured to use the ADC1 channel 4 module.

When I set PA0 high, the ADC readings increase by about 1.8V. When it is low, the readings are correct. Why does this happen? Externally, these two pins aren't connected directly to each other.

Jeroen3:
1.8V is a lot. Either your circuit isn't working as expected, or the board is assembled poorly.

AndyC_772:
What actually happens to the voltage on PA3? Does it change at all when you change the level on PA0?

T3sl4co1l:
Is there any signal bounce on the pin?  (You may need a >200MHz oscilloscope and high impedance probe to verify this.)

Is there any noise coupling into the ADC pin?

Is the ADC signal source a high impedance?

Tim

Throy:
I had a similar problem with a STM32F072.  I had connected one pin that can also be used as an ADC to a 5V transceiver thinking that the pin was 5V tolerant.  Obviously wasn't....  As a quick fix I was able to put current limiting resistor between the pin and the transceiver.  In the next board rev, I relocated the transceiver to a different pin.

Are you using a PNP and if so what is the voltage at the emitter?

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