Design and Analysis of Dual-Mode Digital-Control Step-Up Switched-Capacitor Power Converter With Pulse-Skipping and Numerically Controlled Oscillator-Based Frequency Modulation

Abstract

This paper presents a 3 V-to-5 V integrated dual-mode digital-control step-up switched-capacitor (SC) power converter. The feedback control circuit is equipped with a low-power analog-to-digital converter which monitors and feeds the output voltage to a digital controller. With light loading, the control loop operates in a pulse-skipping mode. With heavy loading, the control loop operates in a frequency modulation mode (FMM) based on a numerically controlled oscillator whose switching frequency varies from 31.25 kHz to 1 MHz. The design is fabricated in a 0.5- μm digital CMOS process. With multiplierless implementation, the controller requires a gate count of less than 300. The whole design occupies a total active area of 0.23 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . From silicon measurement, with a 330-nF external flying capacitor, the design delivers a regulated 5 V output with an output current up to 25 mA from a 3 V supply, delivering an output power greater than 100 mW. The load regulation is measured to be 0.14%. A remarkable efficiency of 80% or above on average under various loading conditions is achieved. Dynamic characteristic and stability analysis of the SC converter in the FMM are presented. Comparisons with existing designs demonstrate the excellence of the proposed design.