High Efficiency High Step-down Ratio DC-DC Converter Based On SC-Buck

With the development of semiconductor technology,the feature size becomes smaller,and the supply voltage required by circuit modules is reduced,even lower than 1V.If the typical input voltage of a portable electronic device is about 10 V,using the conventional Buck converter to achieve a high step-down ratio will result in problems of efficiency and cost of inductance and capacitance.Therefore,the research and design of a monolithic power management chip with high step-down ratio and high efficiency is of great significance.Considering the advantages of switching capacitor circuits as high efficiency,easy integration and low voltage stress,a hybrid topology of switching capacitor and Buck(SC-Buck)is proposed in the thesis,which is suitable for high step-down ratio.A novel hybrid topology is used in the designed chip system.The whole system only needs four power transistors,which greatly saves the chip area.At the same time,only one power switch is in the state of hard switch by optimized timing,which improves the efficiency of the system.The improved peak current control mode is adopted in the control strategy.By analysis and design of the zero and pole in the system,the fast transient response to the change of input voltage and output load can be realized,and the ESR value of output capacitance is not required.Under light load,the zero current detection module is enabled and automatically adjusts the offset voltage.Once the inductance current is zero crossing,the power transistors will be turned off in time.If the load current drops further,the system enters Burst mode to further improve the efficiency of the system under light load.Aiming at the surge problem when power on,the system also has a special two-stage soft start design.In addition,over-temperature protection and over-current protection are designed to ensure the system security.The chip is designed in Global Foundries 0.18μm BCD(Bipolar CMOS DMOS)process.The SC-Buck converter designed in this thesis has an input voltage of 5-10.5V,an output voltage of 1V,and a maximum output current of 4A with a peak efficiency of over 85%.The simulation results show that the chip can start-up normally when the system powers on and has the fast transient response when the load is jumping.The zero current shutdown and the Burst mode under light load also meet the design expectations.