Novel current limit circuitry for LDOs

This paper presents a novel circuit implementation for overcurrent protection of low-dropout voltage regulators, that is able to limit the maximum current the regulator can source into the load to a value set by the user and to keep the current limit value fairly independent of process variation and output voltage, as well as maintaining its temperature drift over the wide temperature range of −50°C to +185°C to below 15%. This is achieved by using an open loop Widlar bandgap structure supplied by an additional current branch, placed in parallel with the power transistor. Design equations are presented in the paper along with electro-thermal simulations that identify the hot spots of the power transistor, thus optimizing the placement of the sense transistor and improving the current sensing accuracy. The proposed circuit is implemented in a standard bipolar junction transistor process. Measurement results — including thermal test scenarios are in good correlation with simulations, thus validating the design.