Design Of A Step-down DC-DC Converter With The Valley Current Mode And Constant On Time Control

With the rapid development of electronic technology, a wide range of electronic products have been seen everywhere in our daily lives, the power management chip is the heart of electronic products, whose performance directly determines the electronic product life time and life. So in order to improve the performance of electronic products,research and development of power management chips become an important task of modern science and technology development. Power management chip is toward low power, low cost, small size, high conversion efficiency of the direction of development.In the power management chip, DC-DC switch-mode power supply with low power consumption, high conversion efficiency, low-cost advantages, but it is difficult to integrate the entire system in a single chip. In recent years, DC-DC Switching Power have been widely used, especially in the use of high-power applications.In this paper, we will design, simulation and achieve a DC-DC switch-mode power with BCD process. This Papers start from the electrical characteristics of the indicators, to design the circuit,and to simulate the circuit, designed a wide input voltage range, wide output voltage range and high current output of the buck DC-DC power management chip.The paper first introduces the development of power management chips, as well as the significance of power management chip, and then introduces three DC-DC(Buck,Boost and Buck / Boost) topology, and detail introduce the principle of the step-down DC-DC, the difference of voltage mode control and current mode control, as well as continuous conduction mode and discontinuous conduction, the difference of three different step-down DC-DC modulation(Pulse Width Modulation,Pulse Frequency Modulation,Mixed Modulation), and the step-down DC-DC stability and compensation network design parameters are analyzed in detail, providing a comprehensive theoretical support for the realization of chip design and simulation.The buck DC-DC power management chip of this paperuses adopt Constant On-Time control, using continuous conduction mode when overloaded,and using forced continuous conduction mode or using discontinuous conduction mode at light load, its efficiency can be as high as 92%. The chip implements a wide input voltage range of 4.5V to 28 V, and a wide output voltage range of 0.6V to 5V, the average current of up to10 A.using the current mode control, so the chip has a fast transient response speed.Chip uses valley current mode control so in the heavy and light load full load range there all will be high efficiency conversion, due to the constant on-time of the chip and the valley current mode control, making the error of the previous cycle does not affect the next cycle, so even in the case where the duty ratio is greater than 50% this chip even not generate sub-harmonic oscillations, the slope compensation circuit is not required. The chip uses a programmable soft-start, the output of the error amplifier comp slow rise at power startup, eliminating the inrush current at power-up. In addition,the chip also integrates a short-circuit protection, overvoltage protection, undervoltage protection and other protective circuits.This paper research on Valley Current Mode and Constant On Time Control buck DC/DC converter chip with a 0.35 um BCD process design, use Cadence spectre software to build the circuit modules of the chip, design and simulation the single module and whole circuit, simulation results show that the single modules and the overall simulation results meet the overall chip requirements,and has a good voltage regulation and load regulation, efficiency can reach 92%. The chip’s overall circuit design and simulation has been completed.