A Light-Load-Efficient 11/1 Switched-Capacitor DC-DC Converter With 94.7% Efficiency While Delivering 100 mW at 3.3 V

This paper demonstrates a 2-phase 11/1 switched-capacitor (SC) DC-DC converter that provides an output voltage V-OUT of 3.3 V from an input voltage V-IN in the range of 37.4 V-39 V. SC converters, unlike their inductive buck counterparts, do not rely on the pulse-width modulation (PWM) duty cycle to set the voltage conversion ratio (VCR) as this is determined by the SC converter topology. Consequently, SC DC-DC converters do not require a very low duty cycle, resulting in a short t(on) for the full-input-voltage-rated high-side switch and significant driver power consumption. Instead, a two-phase SC converter is found to be an excellent candidate for high-ratio voltage conversion as it maintains a 50% duty cycle and exchanges few components of high voltage rating with more that are rated for lower voltage. A hysteretic controller ensures stable operation from 0 mW up to 140 mW under full load-step transients and line regulation in the complete input voltage range. For an output power P-OUT > 20% P-OUT,P-max, the system attains an efficiency above 91%, with a peak efficiency of 95.5% for a 70 mW load from a 37.42 V input. The converter topology requires only five flying capacitors, which is the theoretical minimum, implemented with 0603 ceramic surface-mount device (SMD) capacitors. Next to the 11/1 SC converter, a multiple-input multiple-output (MIMO) auxiliary rail generator is proposed as a uniform technique to efficiently and simultaneously provide a number of auxiliary supply rails, necessary to generate and level shift power-switch driving signals reliably.