Design Of An High Accuracy DC-DC Buck Converter With Fast Transient Response

In recent years, with the increasing requirements of switch converter due to the electronic equipment, especially in the application of distributed power supply system which has a wide range of input voltage and high current load, these equipments usually need the switch converter has a high output precision, good anti-interference characteristics, and fast transient response. Therefore, those converters which have great output precision and fast transient response become the main research direction of switch converter. Actually, the constant on-time control converters which has been widely used in these years are the experts’ research hot spot,because this control mode has a good anti-interference, simple structure of this system, and wide range of input voltage. However, this control mode has many disadvantages at the same time of a lot of advantages, such as the capacitive parasitic series resistance effects on output voltage stability, working frequency change with the input voltage, and low efficiency at light load.To solve those problems, this article studied from the aspects of system control mode of DC-DC buck converters, proposes a high output precision DC-DC buck converter with fast transient response combining with the system design goals. This converter based on the COT control mode, add a Phase Locking Loop(PLL) to control the frequency of this system, combines valley current control mode to achieve the goal of fast transient response. In this system, this paper has designed a working state judgment circuit to improve the efficiency of this BUCK converter when the system needs to working in the standby state or dormancy state. And also, this article has designed some band-gap reference sources with high precision to improve the accuracy of output voltage.This article based on the 0.25 μm BCD process to implement the system working state judgment circuit and band-gap reference sources by using HSPICE and Cadence. And also, this article simulated the state judgment of this system, state working state, linear transient response, and load change transient response. The simulation results show that the system can improve its efficiency effectively with system judgment circuits, have a good output stability when the system working in the stable state, a fast linear transient response when the input voltage changed, and also have a fast load change transient response which can back to the stable state with 25 μs, the output overshoot voltage and under voltage were limited to 90 m V when the load current change, which meet the design requirements of the system.