Research And Design Of A Buck Converter Based On Adaptive Constant Conduction Time

DC-DC converter with its low cost,high efficiency,high reliability and many other advantages,has become the new darling of power management products.To meet a variety of applications,the industry has emerged a variety of different types of power management solutions.The Buck converter based on the Constant On-Time(COT)control mode is simple to design the control loop,with higher energy conversion efficiency,stronger ability to resist noise interference,and low EMI,and other excellent features.However,the system stability and output accuracy based on the COT control strategy still need to be optimized in applications where the output capacitor’s equivalent series resistance(ESR).In this context,this thesis presents a buck converter based on adaptive constant conduction time(ACOT)control mode.For the stability problem,the proposed structure of this thesis through sampling and filtering the switch node voltage information,so as to realize on-chip virtual ripple compensation for the control loop.For the control accuracy problem,an approximate amount is generated in the filtering process to makes the system eliminate the DC offset while compensating the ripple.As ACOT control mode lack of cycle-by-cycle current limit function relative to the peak current mode,the overcurrent protection to ensure the reliability in this thesis.In addition,the ACOT control mode achieves an approximately constant switching frequency in CCM,while improving EMI characteristics.In this thesis,several control modes commonly used in Buck converter are analyzed in detail,and the optimization measures of several key technologies are introduced.On the basis of the theoretical analysis,a corresponding optimization scheme is proposed.Based on the 0.18μm 18 V BCD process,the design of the whole system and each module are completed.Using the Spectre simulation software to simulate each module and the whole chip.According to the simulation results,the chip architecture can achieve high output accuracy,low ESR system stability,fast transient response,constant frequency under CCM mode,high efficiency and other expected performance.