At this year's IEEE International Magnetics Conference in Toronto, Canada, a team from Fuji Electric Corp.'s (Japan) Matsumoto City Research and Development group presented a 1W step-down dc/dc converter fabricated with an integrated planar inductor on a silicon substrate. Based on a combination of semiconductor production technology and micro-machining technology, the goal of the project is to realize a one-chip monolithic power supply that integrates all components onto a single substrate.
The current prototype measures 10mm square (the inductor is 4mm square) and operates at 3MHz. The 5V to 3V converter produces 1W of output power with 80-percent efficiency and a power density of 5.6 W/cm3 (about 90 W/in3). The planar inductor has a sandwich structure, consisting of a 16-turn spiral coil between upper and lower 9µm thick CoHfTaPd amorphous magnetic thin films.
By integrating the inductor on the silicon substrate, along with the PWM controller, two power MOSFETs, an output rectifier and ceramic capacitors, a very low-profile dc/dc converter is realized. Package dimensions after molding of the dc/dc converter into a plastic package are 10mm X 10mm X 1.8mm.
The current converter employs conventional rectification. The addition of synchronous rectification is expected to significantly improve the conversion efficiency. Future goals of this development program are to achieve higher efficiencies, further reduce the size of the assembly, and to establish process technologies necessary for mass production.
