Hi, I didn't know SIO pin has a special behaviour and problem ever.
In other case, PSoC1, I had similar problem of Pin.
That is also related with LED drive.
[ http://www.cypress.com/?app=forum&id=1573&rID=77568 ]
There might have particular issue with Diode,
Current undershoot and Reverse recovery characteristics?
Anyway, we have to use the pin enough within the absolute current limit.
SIO has a special features and drive current ability.
I can't find any description about that issue.
AN60580: [ http://www.cypress.com/?rID=40989 ]
Author: Pavankumar Vibhute
There is a notation of the author.
Would you mind contact with him?
I assume you have re-program the cip, and it still fails.
Hi HL-san, It's a permanent break down.
Yup, I have re-programmed the chip, still doesn't work.
SIO pins have a similar ESD protection as any other pin.
Since you are using CapSense you are bringing out the traces of the port to the outside and that can be the same for the LED. Here you may have experienced a strong static discharge that destroyed the pin's electronic.
I would suggest to view at your board-design to check if a (very) strong discharge could reach the pin's traces.
I would conclude from the below that SIO circuit structure has some
differences. You might post a "CASE" and let the forum know the
“Create a MyCase”
If you suspect specific pins/external interface consider reving board
and adding protection arrays to the pins. ON Semi, Fairchild Semi,
Vishay have smt arrays of zeners/diodes for that purpose.
Bob, how do SIO pins have the same ESD protection if they support higher voltages than the maximum voltage of the microcontroller?
Normally ESD protection is implemented with a diode from the pin input to the voltage rail (one is formed by the inherent body-diode in the top totem-pole MOSFET also).
These SIO pins cannot have a diode here, since it would conduct and clamp the voltage on the SIO pin to the supply voltage + 0.7V.