Design considerations of power MOSFET for high frequency synchronous rectification

Synchronous rectifiers used in high frequency, low output voltage applications are power MOSFETs specially designed to replace the usual output Schottky diodes in order to reduce converter losses. This paper deals with the analysis and design optimization of a synchronous rectifier suitable for applications of 1 to 10 MHz switching-mode power supplies. Three different MOSFET structures were studied and evaluated through detailed 2-dimensional device simulations. The internal parameters are optimized against three major performance factors, namely (1) the recovery time of the body diode, (2) the product of on-state resistance and input capacitance, i.e., the loss factor, and (3) the breakdown voltage of the body diode. Based on the evaluation, the UMOS structure produces the lowest RC loss factor and the shortest body diode reverse recovery. The final design optimization of the UMOS was then carried out and an optimized device is presented as the final design.<
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