An integrated circuit (IC) includes input/output (I/O) ports, each operating using one of a pair of unequal power supplies during normal operation of the IC. A lower supply of the pair of unequal power supplies is required to be used as the power supply for the I/O port when a first input signal to the IC is received from an external source on a first I/O port of the I/O ports. The voltage range of the logic excursions of the first input signal is greater than the range from a magnitude of the lower supply to a constant reference potential. A regulation loop derives a derived lower supply having a magnitude equaling that of the lower supply from the higher supply of the pair of unequal power supplies, and applies the derived lower supply on a power supply node of the first I/O port.