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H753ZI - PIN A2 - ADC

TVan .8
Associate III


I'm using the H753ZI board with 26 ADC inputs on ADC1 & ADC3.
The ADC pins run in DMA circular mode and all inputs seem to work fine except one pin: PA2

PA2 is configured like the other pins: Analog mode, no pull-up and no pull-down


But the pin seems to be connected to the 3V3 pin on CN11. There is only a 1.5k resistance between the two pins, so it looks like it's in pull up mode. When PA2 is not connected to anything, it's at 3.3V. How could this be? Should I put it in pull down mode? Should I connect an external pull down resistor?

I'm driving the ADC pins with an opamp in voltage follower mode as a buffer. With 0V input on the opamp +in, the output of the opamp and pin PA2 go to 0.25V. I'ts not that big of a problem, the ADC still works but it lowers the sensitivity of that pin

I have two boards and both show the same behavior on PA2 (with the same software, so it might be a bug in my software). 




PA2 can have many functions ...

I would do a simple test : make a new project, just with set : clock tree , debug , ADC on PA2 .

Then check whats on the pin with opamp (= low , gnd level) and you know : hardware or software problem.


check first, without power, is there some resistance to VDD or next pin ...? (except the protection diodes)


I use (on H743ZI , H733, H7A3) also PA2 as ADC input, no problem ever.

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TVan .8
Associate III

Thx, great idea. I will try this and post the results