Design methodology for over-temperature and over-current protection of an LDO voltage regulator by using electro-thermal simulations

This paper presents a methodology for designing over-temperature and over-current protection (OTP and OCP) circuits for low drop-out voltage regulators (LDOs). The OTP monitors the die temperature developed within the LDO and disables its output stage when the temperature reaches a certain, user-defined, level (the OTP activation point). If the LDO output current reaches a set threshold (the OCP activation point), the OCP takes control of it, keeping the current value to an acceptable level. The proposed methodology involves running iteratively electrical, thermal and electro-thermal simulations. It addresses three major issues: first, it allows the designer to identify the suitable layout placement of the OTP and OCP sensors, based on the temperature distribution within the LDO power-stage. Second, the OTP and OCP activation points can be set accurately by taking into account coupled electro-thermal phenomena and the unavoidable differences between the temperature and current sensed by the protection circuits and those developed within the worst-case LDO section. Finally, the LDO design can be fine-tuned considering complex scenarios of real-life operation and test requirements. An LDO was designed using this methodology and the paper provides a direct comparison between the expected (simulated) results and measurements performed on the silicon implementation.