Power Supply Equalization Circuit Using Distributed High-Voltage and Low-Voltage Shunt Circuits

Embodiments of an IC protection circuit that protects low voltage supply transistors and circuits within the IC from excessive power supply levels and ESD events are described. A protection circuit situated between the IO pins of the IC and the internal circuitry of the IC includes a voltage drop network and a plurality of shunt circuits to protect the IC against excessive supply voltages and ESD voltages, or other excessive current conditions. Each shunt circuit includes an RC trigger stage and an NMOS shunt stage that are made using low-voltage devices. A protection circuit of the embodiments includes a high voltage IO pin, a voltage drop network to drop a high voltage on the IO pin to a low voltage level on a floating voltage rail, a first shunt circuit coupled between the floating supply rail and ground, an equalizer circuit coupled between the floating supply rail and a low voltage supply rail, and a second shunt circuit coupled to the equalizer circuit through the low voltage supply rail.