Performance Analysis of Trench Power MOSFETs in Synchronous Buck Converter Applications

The purpose of this paper is to comprehensively investigate the performance perspectives and theoretical limitations of trench power MOSFETs in synchronous rectifier buck converters over a wide range of operating conditions. Several trench MOSFET technologies are investigated using a mixed-mode device/circuit modeling approach. Individual power loss contributions from the control and synchronous MOSFETs, and their dependence on switching frequency between 500 kHz and 5 MHz are discussed in detail. It is observed that the power losses introduced by the reverse recovery of the sync-FET body diode become increasingly dominant in the MHz frequency range, which is not taken into consideration by the traditional power MOSFET Figure-of-Merit (FOM) of RDS(ON)×QG. A new FOM of RDS(ON)×(QG +Qrr) is proposed to address this special requirement of low Qrr in emerging MHz switching frequency buck converters.