An Overview of Hybrid DC–DC Converters: From Seeds to Leaves

With the surging demands for higher current at sub-1-V supply level in high-performance digital systems, high-efficiency and high-current-density power converters are essential for system integration. Higher voltage supply buses are emerging for high-current applications to reduce the IR losses on the power delivery networks. Thus, there is a wide voltage gap between the power bus and the digital supply rails at the point of load (PoL). Meanwhile, battery-powered portable or wearable devices favor extremely high-power-density solutions, calling for novel power conversion topologies, which have been the hottest topic in the power management IC area in the past decade. This article reviews the switched-capacitor-inductor (SCI) hybrid dc–dc buck converters from the topology “seeds” to their “leaves.” Here, we define six seeds, they are: 1) three-level buck; 2) double-step down buck; 3) inductor-first buck; 4) always-dual-path buck; 5) buck–buck; and 6) multiple-output hybrid buck. We try to analyze and summarize their pros and cons, and to derive the evolution of the hybrid dc–dc converters, with milestone examples. Then, we share our observations, design intuitions, and suggestions to help the researchers and engineers to pick up and design a new SCI hybrid dc–dc converter.