Research And Design Of Buck Converter Based On ACOT Control Mode

With the increasing popularity of portable electrical equipment,DC-DC converters are required to provide different operation supply voltages for different sub-circuits of the same product,and which should have these performances including high conversion efficiency and high stability.At the same time,with the increasing popularity of consumer electronics,automotive chips and other applications,they should have a wide range of load current and fast speed in operation,and it should be required that DC-DC converter has better load transient response and greater load current range.Based on those,a Buck DC-DC converter with large load current and fast transient response is designed in this thesis.The main contens including:Firstly,based on the analysis of the basic principles of buck DC-DC converters,this thesis highlights the stability and response speed of the constant on-time control mode by comparing different control modes.Secondly,in order to overcome these problems that constant on-time control mode is pulse fre quency modulation and its load capacitor needs enough equivalent series resistance,an adaptive constant on-time(ACOT)control circuit is designed to avoid the change of operaion frequency.A buck DC-DC converter with double loop control is given by introducing voltage loop into the system.At the same time,a built-in ripple compensation circuit is designed to avoide the sub-harmonic oscillation of the loop and the requirement of equivalent series resistance of the capacitor.These deisnged mudules,including built-in output voltage trimming and soft start module,can adjust the start-up time and output voltage by selecting digital bits,and whose output voltage can be adjusted in steps of 10 m V with an accuracy of 0.1%.Finally,based on these designed sub-circuits including bandgap reference circuit,output voltage trimming and soft start module,full-range high-speed comparator circuit,ripple compensation circuit,drive module,error amplifier circuit,linear regulator circuit and protection circuit,a buck DC-DC converter based on ACOT control mode is designed in TSMC 0.18μm BCD process.Simulation results show that the designed buck DC-DC converter achieves these performances including the maximum load current of 5A,the output voltage ripple of 47.9m V when it enters discontinuous conduction mode at light load,and the output voltage accuracy of 0.1%.When the load current jumps back and forth from 2A to 5A,the designed buck DC-DC converter achieves these performances including the output voltage response time of less than 100μs,the output voltage jitter of less than 150 m V.When the input voltage jumps back and forth from 12 V to 20 V,the designed buck DC-DC converter has the output voltage jitter is less than 30 m V.And the designed buck DC-DC converter has a maxium conversion efficiency of 98.5%.