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View Full Version : XC82x/XC83x Cap touch with EMC/RF interference.



LarsonD
Nov 7th, 2011, 06:36 AM
I have a customer that is using a microchip cap touch solution right now and trying to convert them over. They are having issues with the microchip solution having false touch detection based on the EMC from a power supply and RF noise from Wireless remote. What suggestions for layout should I give and other areas to watch out for to make sure our solution converts them over.

tomattila
Nov 7th, 2011, 09:10 PM
This is an extract from a training. Slide 3 should help with the power supply noise.

Juergen
Nov 7th, 2011, 09:12 PM
Capacitive touch sensing is inherently sensitive to interference, mainly radiated interference. Commutated interference can be controlled, crosstalk between tracks can be controlled but radiated interference is very dificult to get rid of. Good shielding helps, ground plane on both sides wherever possible. Capacitive touch pads make a good antenna, thats the main problem. A good software algorithm helps a lot.
When you say Elpis, you mean XC82x / XC83x as it is known to the public?

tomattila
Nov 7th, 2011, 09:28 PM
Make sure the board has a ground plane on the opposite side of every touch pad (use around 20% mesh). That will greatly reduce sensitivity to radiated noise (at the cost of reducing sensitivity to touch a little bit as well). Also, a guard pad can help a lot against radiated interference if there is a pin available for this (see last slide).

LarsonD
Nov 21st, 2011, 10:58 AM
Thanks for the responses. Yes I was refering to the XC82X / XC83X family.