A Transient-Enhanced Output-Capacitorless LDO With Fast Local Loop and Overshoot Detection

Abstract

An output-capacitorless low-dropout regulator (OCL-LDO) with simple structure and fast transient response is proposed for system-on-chip (SoC) applications. A super source follower is inserted into a cascoded flipped voltage follower to drive the power transistor, which forms a fast-local loop for quick turn-on. A robust overshoot detection circuit consuming only leakage current is proposed for fast turn-off. The combination of these two techniques significantly reduce the overshoot/undershoot voltages and achieve fast settling time during load steps. A simple yet effective additional turn-around stage is added in the error amplifier to improve the positive phase slew rate for potential dynamic voltage scaling (DVS) function in battery-operated systems. The LDO is implemented in a 65 nm CMOS process and it can deliver a 20 mA load current with 0.9 V regulated output and 150 mV dropout voltage. It occupies an active area of 0.01 mm $^{\mathbf {2}}$ and can work stably in a load range from 0 to 20 mA with $65~\mu \text{A}$ quiescent current. The measured results show a settling time about 100 ns for load steps from $100~\mu $ A to 20 mA as well as V $_{\mathbf {REF}}$ and V $_{\mathbf {IN}}$ steps.