Design Of Low EMI And High Effiency Buck Converter Based On Peak Current-mode Control

In recent years,with the development and popularization of new-generation equipment such as new energy vehicles and Industry 4.0,higher requirements have been focused on the performance and functions of power management chips in equipment.In the field of automotive electronics and industrial automation,the power management chip Buck converter is required to have the characteristics of high loop stability,low EMI radiation,wide input and output range,high operating frequency,and strong load capacity.This thesis focuses on this application field.Studying the loop stability and EMI radiation problems of BUCK converters is of great significance to the industrialization of power products.In order to select a converter control strategy that meets the requirements,the loops of voltage mode control and current mode control in the linear control mode commonly used in the industry are analyzed,and the corresponding stability compensation scheme is studied.Peak current mode control architecture with strong anti-noise capability.In order to meet the requirement of low EMI radiation,starting from the principle of EMI generation,the transmission path and common control strategy of EMI radiation are introduced,and a spread spectrum modulation mode(SSM)that can optimize EMI in the whole frequency band is introduced.For different application environments,a multimode oscillator is designed in this thesis.The operating frequency of the oscillator can be set by an external frequency selection resistor,and it can also work in external frequency follow mode,frequency foldback mode and spread spectrum modulation mode.According to the selected loop control method,a two-stage fully differential error amplifier with soft-start function is designed.In order to prevent inductor current saturation,the output of the error amplifier has a voltage upper limit clamping function;To solve the problem of sub-harmonic oscillation,a corresponding slope compensation circuit is designed.The slope of the compensation slope can be changed according to the change of the output voltage.In order to reduce the loop transmission delay and meet the requirements of high operating frequency of the system,a high power rail,High-speed PWM comparator is designed.The above scheme adopts the 0.25?m 80 V BCD process to design the circuit,and simulates the function and performance of the converter under the Cadence platform.The current mode control Buck converter control loop designed in this thesis can realize the input voltage in the range of 5.5V-65 V,the maximum output current is 3.5A,and the switching frequency is adjustable between 200 KHz and 3MHz.The simulation results show that the control loop designed in this thesis can guarantee the stability of the control loop under extreme application conditions.The fast Fourier transform(FFT)simulation verification is carried out for the spread spectrum modulation mode.The simulation results show that after the spread spectrum modulation mode is adopted,the noise energy at the fundamental frequency of the switching frequency is reduced by 10.1d B.The noise energy is also significantly reduced at all places,and the design goal is achieved.