Design Of High Current Synchronous Rectified Buck DC/DC Converter

Based on the project"Design technique research of mixed-signal IC for single chip", the paper studies the principle and circuit design of high current synchronous rectified step down DC/DC converter.The paper exhaustively analyses the fundamental principles and the key technique of Buck DC/DC converter. The establishment of Small-signal control models for current model stability and compensation networks is deeply studied. According to the above, a high current synchronous Buck DC/DC converter XD7618 is designed and implemented. Synchronous rectification technique is applied in the chip that advances the efficiency evidently. A novel structure of current mode compensation is presented to eliminate the slope compensation effect on the peak current of the inductor, and a optimize circuit of slope compensation, which can not only insure the loop stability but also effectively reduce the over compensation's influence on the load capability, is designed. XD7618 applies phase-lock loop to realize the function of outer synchronization so that decrease the mixing noise when multi-DC/DC are using, the frequency capture range is from 300 KHz to 2 MHz. Typeâ…¡built-in frequency compensation method is adopted to simplify the peripheral circuit. Furthermore, output detection circuit, over temperature protection, under voltage lock out and over current protection are also integrated in XD7618.After the principle analyzing and circuit designing, based on 0.35um 20V BCD processing, the sub module and the whole chip are simulated by using the EDA tools of Cadence. The results show that the output current is up to 7A and the efficiency is high to 93.8%, the chip gets an excellent performance of load capability.