When CY8C22645 is not powered on, and some other outputs are connected to the GPIO pins, the GPIO itself will be in high impedance mode. But the ESD diodes will conduct from the GPIO to VDD and try to power CY8C22645. This may lead to the ESD diode failing, or the PSoC getting reset frequently. In such cases the addition of a series resistance will limit the current through the ESD diode. The resistance can be around a few hundred ohms.
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