Design And Research Of High-Effiency BUCK Converter Based On Adaptive Constant On Time

With the diversification of the development of electronic product features, the demand of the performance of switching power supply is increasing, at the same time, switching power supply for the domestic market general keep low-end, so it has to face new challenges in technology.To solve these problems, the research purpose of this paper is to design a application in portable electronic products of high efficiency DC-DC step-down switching converter. It is required that both input and output voltages to be wide for this converter, it has faster transient response and is able to sync with the external clock. In order to achieve this goal, this paper adopts the adaptive on-time and valley current mode architecture, at the same time, the converter integrated the difference detection circuit, PLL circuit, one-shot timer, output under voltage and output over voltage circuits, which can effectively ensure the working reliability and improve the performance.Firstly, the basic operation principles and two kinds of modulation mode, PWM and PFM, and three kinds of control mode of the DC/DC converter are analyzed in the thesis, including traditional current mode control, the current mode constant on-time mode control and the adaptive on-time mode control, then the advantages and disadvantages and suitable condition of each control are analyzed, then the paper focuses on the adaptive on-time control mode and the main method to realize the timer. Secondly the internal topolopgy of the system, the typical application circuit, the design index, efficiency design and the operation principle of system are analyzed. Then some part of sub-circuit are designed and simulated, including the on-timer for providing the on-time and the bias circuit for providing the voltage bias and current bias and the level-shift circuit for transforming the voltage and controlling other circuit in error state.In this paper, the function verification and characteristics simulation of the whole circuit are done by HSPICE based on 0.25 μm BCD process. The results show that, the function of softstart, whole working, CCM/DCM load transient, and efficiency in the typical condition. At the end, the layout of some circuits is designed in the paper.