A Single-Inductor 4-Phase Hybrid Switched-Capacitor Topology for Integrated 48V-to-1V DC-DC Converters

Abstract

This paper introduces a single-inductor 4-phase hybrid switched-capacitor (4PSC) topology for integrated high-ratio direct down conversion suitable for point-of-load applications. The proposed topology consists of a 3-phase 4:1 switched-capacitor stage, reducing the switching node swing to 12-V (1/4 of the input) to significantly reduce switching loss, and an inductor to softly charge and discharge the flying capacitors with an extra phase (hence 4-phase operation) with controlled duty cycle to regulate the output voltage to 1V for direct-down conversion. The converter operates with a 4X effective switching frequency, which reduces the ripple/inductance required or switching frequency for better efficiency. With the same output voltage ripples as double step-down (DSD) and 3-level (3L1P) buck converters, the on-time is 4X that of DSD and 3L1P converters, which reduces the challenges in controller design. Lower-voltage (LV) transistors, such as 12-V devices, can be used in some of the switches to significantly improve efficiency. When compared to DSD and 3-Level converters that are state-of-the-art integrated topologies, with the same inductor, output capacitor, and output ripples in the same BCD process, this design achieves: 1) an efficiency comparable or higher than DSD (e.g., ∼3% higher at 48V-1V/5A); 2) along with using only one inductor instead of two for DSD, which can reduce the cost and increase the power density; and 3) much higher efficiency compared to a 3-level buck converter. The 4PSC topology is verified in simulations, showing peak efficiencies of ∼85% and ∼91% in a 180-nm BCD process with 48V-1V and 48V-2V conversions, respectively.