Why CapSense sensitivity difference on 2 of the pins of PSoC 4?

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mish_288636
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Hi, I'm working on a design using the CY8C4245AXI-483  (44-TQFP) , with most pins being used as touch-sensors.  I've noticed that two of the pins (P1[0] (pin 37)  and P1[1] (pin 38) seem to be quite a bit less sensitive than the other pins (they all go to the same-size copper electrodes).  I had to increase the bit count from 10 to 12 and reduce the threshold from 80 to 20 in order to get the same 'touchiness'.  Is there anything unique or different about these 2 pins?  I did notice that they are also Op-Amp inputs, could this be a factor?

Thanks in advance...

-Michael

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Vison_Zhang
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Being dedicate Opamp input pins, P1[0]/P1[1] may have very small different Internal parasitic capacitance compare with other pins, but this won't have so big affection on sensor sensitivity, there should be other reason.  Is other any external cap on P1[0]/P1[1] or different series R value? 

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Hi, thanks for the info, so are there any other things that could cause

this, like the on-chip routing? Is there a way to see where/how it ended

up routing each pin?

Thanks!

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Please confirm the external circuit on P1[0]/P1[1] are the same as other sensors. Actually our PSOC4 DVK CY8CKIT-042 (based on CY8C4245AXI-483 ) also used P1[1] as an touch sensor pin, sensitivity have no no different with other sensors.

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Hi,

So yes, all the external circuits are identical, basically just wires

that go to a connector that go to a separate flex circuit with the

actual electrodes.

Our design has 23 electrodes, Is it possible that some of them had to be

internally routed through a less-ideal way? (Not sure how the PSoC 4

does its internal connections but I know on the PSoC 5, we've run into

this issue). Is there a way to see how it was routed?

Thanks!

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I recommend you enable the BIST(build in self test) option in CSD component, read the Cps of each sensor out, then we can see if the sensor cp of P1[0]/P1[1] is abnormal compare with others. About the analog routing, no customer report CapSense sensor routing have issue(you know we have lots of CapSense customers).

If possible, you can upload your project, we can check if there has issue.

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