Low Profile Superparamagnetic Inductor for Portable Electronics Power Management

This article primarily aims for a high-efficiency and high-power-density power management from the USB-C port to the battery within the next generation portable electronic devices. The hypothesis is that by employing superparamagnetic nanoparticles material, which has high permeability and negligible hysteresis loss, the high-frequency inductor design can be very efficient. Therefore, first, the new core material is characterized in terms of permeability and core loss. A dedicated circuit with mutual inductance compensation is used. The relative permeability at 1 MHz is found to be 12 and the Steinmetz parameters for core loss are $\alpha =1.19$, $\beta =1.99$, and $k_\text {SE}=2353$ for result in W/m$^{3}$ at 1–10 MHz. The permeability change with frequency is highlighted. Considering the fabrication constraint, two coupled inductor structures are analyzed. Due to the very low permeability level, 3-D finite element method (FEM) is used to obtain accurate inductance and coupling factor. The core loss, winding loss, and thermal models are incorporated into the inductor design. After optimization, a prototype is built and tested at 3.5 MHz featuring 84.9% nominal efficiency and 1049 W/in$^{3}$ power density. It can deliver up to 6 A at 4 V output for battery charging. The integrated inductor has a very low profile of only 1 mm height and 90 mm$^{2}$ area.