Research Of Multi-phase Buck Converter Based On Constant On-time Control

With the rapid development of power electronic technology,the performance of mi-croprocessors is getting better and better,and it requires a better power supply perfor-mance.More and more transistors are integrated on the microprocessor,and its operating current also increases.The voltage is also reduced to keep the microprocessor’s power consumption at a manageable level.It is important to provide a fast,high-performance power supply for microprocessors.The voltage regulator（VR）,which is the power sup-ply for microprocessors,is a multi-phase interleaved parallel buck converter,which often works in low voltage,high current,and high load change rate situations.Among the VR control methods,constant on-time（COT）control has been widely used due to its natu-ral stability in DCM and high light-load efficiency.But COT control is prone to have overshoot or undershoot voltage phenomenon due to its constant on-time.This thesis aims to improve the transient response of COT control.In the theoretical research and simulation analysis of current COT control methods,the transient response of RBCOT and V~2COT control based on ripple control is the fastest,but the output ripple is large.But it is easy to generate undershoot voltage and overshoot voltage?current mode COT based on current control has the slowest transient response,but the output ripple is lower,and there is no undershoot voltage and overshoot voltage.I~2COT control has a slower transient response,but has low ripple voltage,no undershoot voltage and overshoot voltage.This thesis is based on the average current mode control method,the detailed mod-eling and derivation of the average current mode control are carried out,the small signal analysis is carried out,and the average current mode control under different proportional and integral coefficients is simulated and verified by SIMPLIS.Analysis and parameter design is carried out on average current mode by PI compensation and type Ⅱ compensa-tion.In this thesis,a voltage loop is introduced on the basis of the average current mode control,and a new VICOT control method is proposed,which can improve the speed of transient response of overshoot voltage.The proposed VICOT control method not only has the accuracy of the current mode control,but also accelerates the response speed of the circuit by introducing a voltage loop.It has been verified by simulation that it has low output ripple and fast transient response speed,no undershoot voltage and greatly reduced overshoot voltage.In order to improve the inherent drawbacks of COT control,the Adaptive Constant On Time（ACOT）control strategy is studied,and the FACOT control is introduced into the VICOT control strategy,which becomes the VIACOT control.In this paper,a VIACOT-controlled Buck converter is designed and verified by simulation on single-phase and two-phase mode.The simulation results show that VIACOT control reduces the overshoot voltage of VICOT control and ensures the speed of the circuit returning to steady state.