Design of Fast-Locked Digitally Controlled Low-Dropout Regulator for Ultra-low Voltage Input

This paper proposes a new design for a fast-locked digitally controlled low-dropout regulator (FDLDO) for an ultra-low voltage input. The proposed design involves a fast-locked control mechanism that reduces the settling time of the load transient response in the tracking mode and decreases the quiescent current in the regulating mode. For an ultra-low input voltage of 0.35 V, the proposed FDLDO is capable of providing a regulated output voltage of 0.3 V with a dropout voltage of 50 mV and delivering a maximal load current of 2.4 mA with current and power efficiencies of 99.74 and 85.49%, respectively. Measurement results showed that in the regulating mode, the quiescent current is only 5.15 μA\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upmu \hbox {A}$$\end{document} for the maximal load current; furthermore, for the maximal load current, the load regulation and the line regulation are 1.5 mV/mA and 4.916 mV/V, respectively. Under the load regulation, the transient response time is less than 15 μs\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\upmu \hbox {s}$$\end{document}. No external output capacitor is required to stabilize the control loop, and there is no external input clock. The proposed FDLDO is suitable for low-power system-on-a-chip applications of wearable electronic devices with an ultra-low supply voltage.