21.9 A 20MHz & 1MHz Dual-Loop Non-Uniform-Multi-Inductor Hybrid DC-DC Converter with Specified Inductor Current Allocation and Fast Transient Response

High-efficiency, high-power-density, and fast transient response DC-DC converters are in high demand for consumer, automotive, and industrial applications. In recent years, many integrated hybrid converters have been developed to enhance efficiency and current density [1]–[4], in which the series-capacitor buck (SCB) converters [3] and [4] are particularly favored for their relative simplicity. Figure 21.9.1 (left) shows the Dickson SC hybrid Buck converter (DSC-HB) [5], which offers the advantages of inherent inductor current balance and reduced inductor voltage stress. To mitigate high-voltage device switching losses, converters with high voltage conversion ratios typically operate at lower switching frequencies, resulting in a reduced loop bandwidth (1/1 0-to-1/5 of the operating frequency) and requiring larger inductors. This constrains the inductor current slew rate during load transients and deteriorates the transient performance. This limitation is pronounced in DSC-HB topologies, where multiple output inductors cannot simultaneously increase current during transients. Previous works [6] and [7] addressed this limitation by simultaneously activating all inductors, achieving a 2x increase in the inductor current slew rate and improving the load transient performance. However, for load step-down transients, the inductor current's falling slew rate is still constrained by the low $\mathrm{V}_{\text{OUT}}$ and large inductance.