A CMOS compatible smart power synchronous rectifier

Abstract

The power MOSFET functioning as a synchronous rectifier is a preferred choice in switch-mode converter circuits, especially for those of high frequency, high power density and low output voltage. However, its scope of application is handicapped by the compulsory requirement of additional sensing and gating circuits which provide the precise turning on/off timing control. A smart power synchronous rectifier (SPSR) is a two-terminal diode-like power integrated circuit (PIC) which provides very low on-state voltage rectification without the need of adding external gating control. In this paper, the design and fabrication of a fully CMOS-process compatible SPSR device is presented for the first time. The device had been successfully fabricated and its laboratory measurements indicated that the fabricated prototype has achieved a low forward voltage of 0.18V in comparison with that of 0.25 V for Schottky diode and 0.72 V for the body diode at the same current density of 150A/cm2. Also, the device has a low specific input capacitance of 11.8nF/cm2 as measured, which makes it suitable for the high frequency operation of above 1MHz. The proposed SPSR configuration is suitable for CMOS fabrication process and can be integrated with on-chip dc/dc power converter circuit on the silicon substrate.