11.1 A Direct 12V/24v-to-1v 3W 91.2%-Efficiency Tri-State DSD Power Converter with Online VCF Rebalancing and In-Situ Precharge Rate Regulation

In industrial and automotive applications, 12V/24V power systems are widely used. In such systems, high step-down DC-DC converter is highly desirable to deliver a wide range of current directly to the point of load for high power density and efficiency [1]. In this scenario, the conventional half-bridge topology faces severe challenges of extremely short on-time and highly unbalanced power losses between high-side and low-side switches. On the other hand, switched-capacitor (SC) topologies exhibit obvious drawbacks on insufficient current handling and discrete conversion ratios (CRs). Recently, Hybrid topologies have been presented to use SC topology at the front-end to lower the high VIN voltage stress across power devices, and then use inductive topology at the back-end for current delivery. Accordingly, the inductor size can be greatly reduced to improve system density and low voltage rating devices are used for high efficiency and fast switching. Among hybrid topologies, 3-level [2] and double step-down (DSD) topologies [3] are popular examples, as shown in Fig. 11.1.1. However, 3-level topology uses two low-side switches to discharge inductor, largely increasing conduction loss for high input voltage (VIN) and CR. On the other hand, increasing VIN imposes high voltage stress on switch SH2 in DSD topology, compromising the reliability. At high switching frequency, very short on-times in both topologies make gate drive and feedback loop design highly challenging at high CRs.