Core Size Scaling Law of Two-Phase Coupled Inductors – Demonstration in a 48-to-1.8 V Hybrid Switched-Capacitor MLB-PoL Converter

Conventional design of coupled inductors is focused on a specific converter topology, and the size advantage of coupled inductors over uncoupled inductors is rarely analyzed systematically. This work models the core size for generalized two-phase gapped coupled inductors and provides an effective way to compare the core size for different duty ratios (corresponding to different topologies) and different coupling coefficients. Both the analytical model and hardware prototypes are provided to demonstrate a significant size reduction by using tightly-coupled inductors in hybrid switched-capacitor converters with a large duty ratio. The proposed coupled inductors are applied in a Multi-Level Binary (MLB) Point-of-Load (PoL) converter, achieving 94.4% peak system efficiency and 474 W/in3 power density with 48-to-1.8 V conversion and 60 A output. Both the efficiency and power density are higher than the conventional MLB-PoL converter using discrete inductors.