Research Of Synchronous Buck DC-DC Converter Based On Adaptive On-Time Control

With the development of power electronics and integrated circuit technology,various electronic products are developing in the direction of intelligence,multi-function and highefficiency.The requirements for power supplies are becoming more and more diversified.For different application scenarios,it is necessary to design power management chips with different characteristics.DC-DC converters have been widely studied and applied due to their small size and high conversion efficiency.In this thesis,a synchronous step-down DC-DC converter based on adaptive on-time control is designed.The converter adopts an improved adaptive on-time control method,which can not only improve the transient response speed but also automatically adjust the switching on-time according to the input and output voltages,thus ensuring a constant switching frequency in continuous conduction mode and improving the frequency stability of the system.The RC network used in this thesis can sample the full-period inductor current with high precision.Moreover,the obtained sampled voltage also contains the information of the output voltage,which can further improve the control accuracy of the converter while reducing the complexity of the circuit design.In addition,due to the introduction of the inductor current zero-crossing detection circuit,the system can automatically enter the discontinuous conduction mode under light load.This can efficiently control the reverse flow of the inductor current and reduce the switching loss by reducing the switching frequency at the same time,thereby improving the conversion efficiency under light load.Finally,the system also integrates several related protection circuits,which can further improve the reliability of the converter.The basic working principle of the buck converter is firstly introduced in this thesis.And then the advantages and disadvantages of several different modulation methods and control modes are compared and analyzed.The main power sources of the converter are also discussed,additionally.Through the small signal modeling of the buck converter system,a suitable compensation network is designed to ensure the stability of the system.Based on the index requirements and the control scheme of the system,several key control modules and protection circuits are designed and analyzed.Simulation results show that the performance of these related sub-modules and protection circuits can meet the design requirements well.Finally,the overall simulation of the converter is carried out to verify the performance of the system.The proposed buck converter is implemented with a 0.18 ?m BCD process and simulated on the Cadence Spectre platform.From the simulation results,the input voltage range of the converter is 3?5 V and the output voltage range is 1.2?3.6 V.The maximum load current is1 A and the output current can be limited to less than 1.5 A when overload occurs.The switching frequency in continuous conduction mode is 1 MHz and the maximum conversion efficiency is not less than 95%.In general,the adaptive on-time controlled current mode buck converter designed in this thesis has low power consumption and fast transient response,which can provide certain reference value for the design of power management chips in portable electronic devices.