High frequency inductor design and comparison for high efficiency high density POLs with GaN device

High operating frequency and integration technique are two main approaches to achieve high power density for the switching mode power supply. With the emerging Gallium-Nitride (GaN) based power transistors, the switching frequency of a Point-of-Load (POL) converter can be pushed to several Mega-hertz, while the efficiency is still maintained more than 85%. In this paper, the low profile LTCC magnetic substrate are designed for a 5 MHz, 12 V to 1.2 V, 15 A, 3-D integrated POL module with GaN device. Different LTCC ferrite materials and inductor structures with different number of turns are considered and compared for this high frequency and high current POL application. With the LTCC inductor substrate and GaN device, the 3-D integrated POL module can achieve as high as 1kW/in3 power density and 84% efficiency at 15 A output current. As a benchmark, a SMT discrete inductor is designed and customized utilizing the commercial Ni-Zn bulk ferrite material. The comprehensive comparison demonstrates several benefit of the LTCC inductor substrate, such as ultra-low profile, capability of integration and the light load efficiency improvement.