Design and Performance Evaluation of Hybrid-Switched-Capacitor Voltage Regulators for 48 V to Point-of-Load Application

This paper introduces and compares the single-stage and two-stage hybrid-switched-capacitor voltage regulators for 48 V to point-of-load application. The single-stage solutions are multi-phase series-capacitor buck regulators that equally divides the input voltage to reduce the voltage stress and switching loss. The two-stage solutions utilize unregulated switched-capacitor converters to generate a intermediate bus. The intermediate bus voltage can be 1/2, 1/3, or 1/N of the input voltage depending on the circuit topology of the first stage. The second stage is a multi-phase series-capacitor buck regulator similar to the single-stage solution. The decoupling capacitors are removed and the flying capacitors of the first stage are reused as the input capacitors of the second stage to achieve higher power density. The semiconductor device rating, passive component size and efficiency of the single-stage and two-stage topologies are evaluated as a guideline of selecting the intermediate bus voltage and the stack number of the series-capacitor buck regulator. The analysis shows that the single-stage solutions have higher efficiency, lower device count, but require more capacitors. A48V to 1 V six-phase series-capacitor buck prototype is designed and tested to verify the theoretical evaluation.