Hardware design guide
KE15Z Touch Sensing Interface, User's Guide, Rev. 0, 12/2016
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NXP Semiconductors
2.
Q: If I use SSC in the self-mode and change SSC charge time, can I see some difference, is that
changing the result?
A: In the self-mode, changing the SSC charge time won’t affect the final scan result, but changes
the total scan time as it changes the switching clock frequency. While in the mutual mode,
changing the SSC charge time will change the Rx signal coupled from Tx channel, and will
affect the final scan result.
3.
Q: How to set the parameters of the decimation, order and cutoff in TSI_SINC register properly?
A: These parameters affect the final accumulated TSI scan result, and the scan time as well. For
cost efficiency, setting decimation 8, order 2, cutoff 0 is recommended.
4. Hardware design guide
4.1. Electrode shapes
4.1.1. Electrode shapes for self mode
To maximize the electrodes area from the capacitor plates, it is recommended that the size of the
electrode be similar to a human finger (10×10mm is considered a good size).
Electrode shapes for self-mode
4.1.2. Electrode shapes for mutual mode
The following figure is the recommended mutual key shape. Please note that the numbers of finger has
much impact on the touch sensitivity. In general, more fingers result in stronger noise immunity but less
touch sensitivity. Customer should select the right finger numbers for the thickness of touch overlay. For
example, if the touch overlay is 3mm in thickness, 4 fingers is the best choice. If the touch overlay is
2mm in thickness, 5 fingers is ok.
