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State-Space Switching Model of Modular Multilevel Converters

Fig. 1. Power density of POL converters.
This overview paper focuses on state-of-the-art technologies and trends toward the integration of point-of-load (POL) converters. This paper encompasses an extended survey of literature, ranging from device technologies and magnetic materials to integration technologies and ap-proaches. This paper is organized into three main sections.

  1. Device technologies, including the trench MOSFET, lateral MOSFET, and gallium nitride (GaN) high electron mobility transistor, are discussed along with their intended applications. The critical role of device packaging to high-frequency integration is also assessed.

  2. Magnetic materials: In recent years, a number of new magnetic materials have been explored to facilitate magnetic integration for high-frequency POL converters. These data are collected and organized to help select magnetic material for various frequency ranges.

  3. Integration methods, which are defined with the focus on magnetic integration techniques and approaches. Two integration levels are classified; namely wafer level and package level. Detailed information is presented for each integration level to identify a suitable current scale and frequency range. Three-dimensional integration, which uses a magnetic component as a substrate, is one of the promising integration methods. By using an integrated GaN device and a low-profile, low-temperature co-fired ceramic inductor substrate, the power density of the latest 20-A 5-MHz 3-D integrated POL converter is demonstrated as high as 1100 W/in3, which is an improvement of a factor of 10 compared to industry products at the same current level.