what are other column-row configurations for matrix PCB layout supported by MPR121, other than what is in AN4600?
In other words, can I design 4 columns (ELE0-ELE3) and 8 rows (ELE4-ELE11)?
AN4600 recommends block size 3.5 - 4.00mm. is that side dimension of the block?
What is the max thickness of cover for the sensor?
Is cover must be adhered to PCB?
Can there be air gap between PCB and cover?
Thanks for using our community. There are no "supported configurations" for the MPR121, you can use the configuration that better fits in your application, the only thing that would change is the interpolation algorithm and that would totally depend in your matrix array.
The minimum recommended area for the electrodes is 3x3mm.
All your questions can be answered with the following application note:
Hope it helps.