A high-power-density low-profile DC-DC converter for cellphone battery charging applications

This paper introduces a high-power-density low-profile dc-dc converter for cellphone battery charging applications. The converter delivers 40 W across a 4:1 input voltage range with a nominal input voltage of 12 V and a nominal output voltage of 4 V. The PCB area of the converter is limited to 80 mm² and the component height is limited to 1 mm. Three alternative topologies - a zero-voltage switching quasi-square-wave (ZVS-QSW) buck converter, a three-level buck converter, and a resonant switched capacitor converter are analyzed and compared in terms of efficiency and power density in this application. The magnetic components of the converters are designed and optimized as planar structures with custom-shaped ferrite cores. The ZVS-QSW buck converter is predicted to achieve the highest efficiency under the area and height constraints. A prototype 1-MHz ZVS-QSW buck converter with a PCB area of 79.6 mm² and component height of 1 mm, designed for an input voltage range of 5 V-20 V, an output voltage range of 3 V-4.2 V, and a maximum output current of 10 A is built and tested. The prototype converter achieves a peak efficiency of 96.7% and a power density of 3230 W/in³.