Novel Twisted Core Hybrid Coupled Inductor for Vertical Stack Voltage Regulator Module

The high-performance processor's power demand is ever-increasing, necessitating many small, fast, and efficient voltage regulators. Vertical-stacked voltage regulator modules (VRMs) have been used to save the precious processor card's real estate. The multiphase negative coupled inductor helps the voltage regulator to achieve better transient performance without sacrificing efficiency. This article proposes a novel twisted core inductor structure with a straight phase inductor winding that simultaneously enables negative coupling and ultra-low winding resistance, which is attractive for high-current vertical-stacked VRMs. Different twisted core structures are discussed, and design examples are provided. This article further proposes a technique to implement the hybrid-negative-coupled inductor (HCL) topology using the proposed twisted core inductor structure as the unit cell to couple between any even number of phases symmetrically. Therefore, the benefit of negatively coupling many phases can be leveraged. Four twisted core units are built, each capable of handling up to 160 A load current, achieving a high current density of 2.54 A/mm$^{2}$ with a height of only 5 mm. The steady-state and transient performances of four-phase and eight-phase coupling are experimentally compared, demonstrating the benefits of a larger steady-state inductance with a greater number of coupled phases while maintaining a small transient inductance.