Patent ID: 11165417

Abstract:
A circuit to protect a digital input and output (I/O) terminal from an overvoltage applied externally to the digital I/O terminal. The circuit is arranged similar to a bootstrap switch such that a pass-device protects an output driver from an overvoltage applied to the digital I/O terminal and the output driver controls the operation of the pass-device, such as an N-channel metal-oxide semiconductor (NMOS) transistor. The circuit may include a capacitor and a diode coupled to the gate of the NMOS transistor. A digital zero from the output driver charges the capacitor. A digital one from the output driver causes the charged capacitor, coupled between source and the gate of the NMOS transistor, provides sufficient gate-source voltage to pass the digital one from the driver to the digital I/O terminal. The circuit further includes refresh circuitry configured to maintains the gate source voltage on the capacitor.