A Research Of BUCK DC-DC Converter With Wide Load And High Efficiency

In the modern electronic devices, power management chip is an indispensable and important component. With the development of modern technology, the power chip need to provide bigger output current. At the same time, high efficiency is also the basic requirement of power management chip.This paper have designed a wide range of output, high efficiency, peak current control mode of synchronous rectification BUCK DC-DC converter. The adoption of new type of lossless DCR sensing, to avoid plusing a sensing resistance, reduce the conduction loss of converter, and it significantly increased efficiency under the condition of large current output. In this paper, the chip has three work modes at the condition of light load: burst mode, pulse-skipping mode and forced continuous mode. Burst mode has the highest efficiency and the worst of ripple. The efficiency of the forced continuous mode is the worst but has the best output ripple, and pulse-skipping mode is a compromise. According to different demand, different work mode under light load can be chosen. Synchronous rectifier technology can improve the efficiency because of the lower conduction voltage drop of the NMOS, this article also designs the dead time for synchronous rectifier technology. Bootstrap capacitance can ensure NMOS switch power tube fully conducting, reducing the conduction loss. In addition this paper also have designed a slope recovery circuit, to offset the loss of the maximum output current caused by slope compensation, improving the load capacity of the converter.This paper firstly introduces the switching power supply chip research background and significance, then introduces the basic working principle of switch power converter, and several basic categories. Then several kinds of classification and sources of the loss of switch power converter is anlayzed, to lay the theoretical foundation for the rest of the article. This paper introduces several kinds of the methods to improve the efficiency of the converter, including the synchronous rectifier and dead-time controlling, DCR sensing technology and three work modes under light load. Then the dissertation designes and analyses the basic module and some important circuits, and the simulation verification and various parameters are given. Finally this dissertation set up a system simulation for the converter circuit, then the function verification of converter system and the key parameters of the simulation are given.We use CSMC / 40 V BCD process and Cadence and HSPICE simulation tool for chip internal module and overall performance simulation. Simulation results show that the system can work normally, and all performance meet the design requirements. Its maximum output load current is 20 A,and the highest efficiency can reach 93%. The overall electrical characteristics simulation results show that the chip meet the design requirements.