TSC problem when enabling Vdda

Hi,

I'm developing a project based on the STM32U535VET, in which I have 12 touch buttons and a TFT display.

Starting condition:

I'm in a situation in which I'm reading the TSC channels and I'm having some "analog" problems. If the Vdda isn't enabled, the TSC seems to work correctly and the TSC channel waveforms are what I expected, i.e. the quare wave charging the electrode capacitance Cx goes from 0 to Vdd=3.3V at the beginning of the channel charging time, thus the sampling capacitor Cs charges in a certain time (see image D000, in which the blue channel is the Cx voltage and the red one is the Cs voltage).

Problem 1:

As soon as the Vdda is enabled (using HAL_PWREx_EnableVddA()), all the TSC channel waveforms are modified in the same way: the square wave charging the electrode capacitance Cx goes from about 0.6V to Vdd=3.3V at the beginning of the channel charging time thus the sampling capacitor Cs charges in a longer time (image D001).

Problem 2:

In this condition with TSC and Vdda enabled, if I toggle a digital output having the maximum output speed set to a value different then LOW, all the TSC channel waveforms are further modified in the lower part of the electrode capacitance Cx charging time (image D002). This happens only during the digital output switching activity. When I stop the digital output toggling, the TSC channel waveforms goes back to the shape described in Problem 1.

Do you have any suggestion?

Thanks a lot,

Alessandro