TSC Advice please

[Lanceh]

Hi, I am working on an IR remote using STM32L412RBT6P. I have the touch sensing system working to provide the buttons for the user. The user touches a button to send an IR (RC5) code and an LED flashes to let you know it happened.

Q1:I have one touch channel that holds the pressed condition for 2 to 3 times longer than the the others. You can clearly see this in Cube Monitor when looking at the Delta's. You can see the channel 3 (Red) is holding the touched condition longer in the attached image. All touches are as similar as I can do. All sensors and PCB tracks are very similar to each other. What effects the duration of the touched condition?

This channel is connected is TSC_G2_IO1 (PB4). After laying out the PCB I discovered UM1913. This recommends PB4 is only used for the active shield, which I have allocated to TSC_G1_IO1, Shield and IO3, Capacitor. Does this contribute to the longer touched time?

Q2: I am currently running the clock at 20MHz. If I reduce it 2MHz to get into Low Power Run Mode are there any issues with the touch system I need to be aware of?

I recall reading the clock should not be too high for the TSC, have found no recommendations about the lower frequencies.

Any advice gratefully appreciated.

Thanks in advance, Lance.

[Stassen.C · Accepted solution]

Hello Lance,

Yes PB2 should be used as either an active shield or sampling capacitance only depending on the package you have and that is why you see a longer pulse.

For the 2Mhz you should be fine

Regards,
Stassen

[Lanceh]

Thanks Stassen, the new board is be made now. I hope to report back the problem is solved and I have not added any problems soon.

Regards, Lance.