about touch pad layout of MPR121 touch sensor IC

[hakjinjeong]

Hello,

I am using MPR121 touch sensor IC.

According to your application note( AN3747- Pad layout application note),

Traces for capacitive sensors should never be routed under other electrodes.

My PCB is not so big, I have difficulties in layout design.

My questions are those.

1) Can I route other traces (not for electrodes) under the electrodes?

    - like LED controls lines (low frequency signal)

2) also can I put components like resistors/capacitors under the electrodes?

Thank you for yout help in advance.

Best Regards

Hak-Jin Jeong

[reyes]

Hi guys,

It is not recommended to place any components and/or traces underneath the touch sensing electrode's area avoiding electrical noise to be capacitive coupled to the electrodes, especially in two layer boards. If more layers are available on a board, placement opposite to the electrode is possible with appropriate electrical isolation provided by the ground planes.

In both cases, good results can still be obtained if the number of components behind the electrodes is minimized and limited to passive devices and running as few traces as possible.

It’s also important to mention that it is recommended to use X-hatch land pattern underneath the electrodes area.

For more recommendation about the electrodes design and layout I would recommend you to read the application note AN3863, it’s more complete and updated than the AN3747.

Have a great day,
Jose Reyes

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[kharylambie1]

hak can you get back to me i am doing some touchpad design and would like to talk to you skype khary.lambie