Question: I have no alternative but to be able to handle 5V applied to the I/Os on the PSOC with Vss=Vdd=0. What's the maximum current that can be clamped by the chip's I/O protection diodes?
Response: The over voltage protection current that the diode can handle is under 200mA. At 200mA and up the part will latch up. Thermal conditions must be considered also -- the PSoC die temperature cannot exceed the specified range. Diodes run from the I/O pins to Vss and to Vdd. Refer to Section 3 ?Absolute Maximum Ratings? of datasheet for your PSoC part number for further information.
Keywords: protection, diode, maximum, current