SEMICONDUCTOR POWER SEMINAR 2008 - 2009 1 MOSFET Selection to Minimize Losses in Low - Output - Voltage DC - DC Converters

This paper focuses on the role of the power MOSFET in achieving high-efficiency converter design. It provides a brief overview of current low-voltage MOSFET trench technologies, along with a discussion about onresistance versus gate charge trade-offs for MOSFETs optimized for use as control or synchronous switches. It covers the importance of the integrated Schottky diode (SyncFETTM MOSFET) in synchronous rectification and the necessity for packaging technologies with low parasitic inductance and resistance. The MOSFET-to-circuit interaction is discussed in detail, with TCAD mixed-mode simulations. All relevant MOSFET switching events are analyzed: common-source inductance versus drain current rise and fall, body diode conduction and reverse recovery, external Schottky diode layout challenges versus SyncFET MOSFET advantages, and elimination of shoot-through currents from gate bounce. The simulated MOSFET power losses are compared for various circuit inductance cases and used for background in discussing measured converter efficiency data. A review of popular MOSFET loss equations is also discussed.