A High Density Three-Level Quadratic Buck Hybrid Converter for 48V-to-PoL Conversion

This paper presents a new hybrid topology for 48V point-of-load (PoL) DC-DC converters. The proposed three-level quadratic buck converter (3LQB) consists of a three-level buck converter at the front-end merged with an inductor-first buck converter to achieve the required high ratio conversion with only 6 switches. The three-level buck stage allows for the reduction of the inductor value, while the inductor-first buck stage takes advantage of parallel paths through two inductors to deliver more power, with phase interleaving that results in smaller ripples at the output. These two factors combined contribute to improvement of efficiency and density, while the quadratic duty-cycle to voltage conversion relation provides the benefits of duty-cycle extension needed for high-ratio voltage conversion. The measured peak efficiency for a 48V to 1-3.3V conversion using GaN switches is 89.4%, 91.1% and 93.5%, and the power density is calculated to be 1kW/in³, 1.5kW/in³, and 3.3kW/in³ for an output of 1V, 1.5V and 3.3V, respectively, with a max load current of 45A.