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TSC problem when enabling Vdda

Associate II


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,



ST Employee

Hello Alorenzato,

Could please share with us your TSC configuration? Or your project so we can help?


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Associate II

Hi Stassen,

I already opened a ticket with ST support and 'll share the info here as soon as we solve the problem, but I can share the project with you anyway. See attached folder. You can find the instructions to repeat the problem in main.c, after the pheripheral initialization functions.

Thank you!


Christian N
ST Employee

Hello alorenzato, 

Thank you for contacting STMicroelectronics.

Your post was escalated to ST Online Support Team for additional assistance.

Kind Regards,


ST Support

ST Employee

Dear @alorenzato ,

Thank you very much for the escalated case, after investigation. we confirm the behavior as a silicon limitation and my colleagues will be back to you on the Online support case Opened on the fix plan soon and update of our existing errata on the ADC 2.2.14 with this use case.  Thank you again !