Will driving the I/Os of an unpowered bank cause damage to the part?
How much current can the clamp diodes sink?
When driving an I/O in an unpowered I/O bank, there are two aspects of the device specifications that must be considered:
Clamp/ESD diode threshold will range from 0.43 to 0.64V. The worst case of 0.43V is at Tj = 100deg C. An unpowered part will remain close to ambient temperature.
For a C grade device, with Tj = 85 degrees C, assume diode drop = 0.53V. Then, Vcco could be reverse powered by Vin up to the Maximum Vcco- Diode drop at Tj = 85 degrees C (that is, 3.465V - 053V = 2.935 V).
At 85 degrees C, this condition could affect long-term reliability of the device if the power distribution system of the PCB does not sink enough current.