Current sense circuit with electrostatic discharge protection

Abstract

A circuit that allows for accurate power transistor current sensing and electrostatic discharge protection. The circuit includes a power field-effect transistor and a sense field-effect transistor. The sense transistor current is proportional to (but much smaller than) the power transistor current. Thus, the power transistor current may be measured by measuring instead the sense transistor current. The gate nodes of the transistors are connected together, and the drain nodes of the transistors are connected together. However, the source nodes of the transistors are not directly connected to each other, and are instead connected together via a protective resistor. When the circuit is exposed to electrostatic discharge at the source of the sense transistor, the influx of charge that would have otherwise damaged the sense transistor is instead shared between both transistors via the protective resistor.