An NMOS LDO With TM-MOS and Dynamic Clamp Technique Handling Up To Sub-10-µs Short-Period

Abstract

A current-efficient and fast-transient n-type low- dropout regulator (LDO) for high-frequency load transient in mobile phone applications is presented in this article. By using transconductance magnified MOS (TM-MOS), it reduces LDO’s output impedance with fast response speed and keeps high current efficiency. Moreover, based on load-current sensing of TM-MOS, active clamp strategy is implemented to optimize the driving dead zone (DDZ) of this NMOS LDO and achieve good high-frequency load transient performance. Robust loop stability for a wide load-current range is ensured as well with the help of revised Type-II frequency compensation. This circuit has been implemented in a 0.35-µm standard CMOS process and occupies an active chip area of 470 × 280 µm2. With a 1-µF output cap and load steps between 0 A and 300 mA, experimental results show that it features 50/36 mV of under- shoot/overshoot at low-frequency load transient and 68/36 mV of undershoot/overshoot at the high-frequency load transient (i.e., 10-µs light-load duration). This regulator consumes 8.2-µA quiescent current, achieving 99.68% equivalent current efficiency at 300-mA load current.