Research On High-efficiency Buck DC-DC Converter Based On ACOT Control

In the rapid development of integrated circuits today,the size of the chip in accordance with Moore’s Law is becoming smaller and smaller,portable electronic products such as smart phones,computers,etc.continue to shrink in size.Power supply as a key component of electronic products,with the development of integrated circuits power management chip performance has also moved to a new level.Among them,the DC-DC converter stands out in various electronic devices due to its many advantages such as high efficiency,low output ripple and low power consumption.Designing a DC-DC converter chip with miniaturization,high stability,high efficiency and fast transient response is the main content of this research thesis.The use of DC-DC converters is expanding,and the control methods used in different applications are different.At present,there have been more mature voltage control mode and current control mode technology research at home and abroad,which are eliminated due to their complex circuit design and poor system stability.The COT control mode has important theoretical and practical significance because of its simple loop structure and fast transient response.However,the COT control mode has problems in system operation such as unstable operating frequency and the need for large output capacitance,which seriously restrict its application in the market.In order to improve the defects of COT control mode to achieve higher performance,this thesis proposes a high efficiency Buck-type DC-DC converter based on ACOT control mode,which can not only improve the transient response performance of the system but also overcome the defects of COT control mode,which can make the on-time of the switch automatically adjust with the change of input and output voltage to ensure that The converter not only improves the transient response performance of the system but also overcomes the shortcomings of COT control mode.Under light load conditions,an inductor current over-zero detection circuit is introduced into the converter,enabling the system to automatically switch to PFM modulation mode,effectively preventing inductor current backflow and improving conversion efficiency.At the same time,in order to further improve the reliability of the system,a protection circuit is integrated into the converter.Firstly,the basic working principle of the Buck DC-DC converter is explained in detail,the advantages and disadvantages of several common modulation modes and control methods are compared and analyzed,and the main power consumption sources of the converter are discussed.Finally,the ACOT control mode is adopted,and the converter can be switched to different modulation modes under different load conditions to achieve a better performance.Based on the system design index requirements and the related control scheme,the key sub-module circuits of the converter are designed and analyzed in detail,and the simulation results show that the relevant sub-modules can meet the design requirements.Finally,the overall simulation of the converter system is carried out to verify the correctness of the overall circuit function.This thesis is based on the CSMC 0.18μm BCD process to complete the design of the device parameters of the overall system,and the Cadence Spectre platform to simulate and verify the submodules and the overall system.The verification results show that the converter has a wide input voltage range of 3.5V-5.5V,can output a stable low ripple voltage of 1.5V,can bear a maximum load current of 2A,and has a constant switching frequency of 1MHz under CCM,and under DCM,the system enters into PFM modulation mode with a reduced operating frequency,and the conversion efficiency is not less than 79%.The ACOT-controlled Buck converter studied in this thesis has the characteristics of high efficiency,fast transient response and low output ripple,etc.The simulation results show that the converter has achieved the expected design goal,which has practical reference significance for the study of power management chips in electronic products.