Design Of Low-EMI Wide-input BUCK Converter Based On Current-mode Control

With the rapid development of the integrated circuit industry,power management accounts for an increasing proportion in the global semiconductor market.As an important part of power management,switching power supply has become an important research direction.Due to the rapid development of portable electronic equipment and consumer electronics,the development trend of switching power supplies is high integration and low EMI.This thesis aims at a synchrono us buck converter applied in the field of automotive electronics.Combining the trend of low EMI characteristics of with a switching power supply with BUCK converter,this thesis designs a buck converter with a wide input range and Low EMI characteristic.In order to determine the control strategy of the BUCK converter,the peak current mode and current mode COT of the two most commonly used control modes in the industry were compared.According to the goal of low EMI,a peak current with constant switching frequency and stronger noise immunity was selected.In order to achieve the purpose of low EMI,the principle of EMI generation is studied,and the source of EMI of the BUCK converter is analyzed.Spread spectrum technology is used to suppress EMI noise.An oscillator module capable of synchronizing the external clock frequency is designed for a wide input application range.Different switching frequencies and slope compensation slopes can be achieved through external frequency selection resistors.The Spread spectrum module is designed to introduce the frequency variety cooperate with the oscillator module,and the duty cycle changes after the spread spectrum is introduced are studied.The errors in the conclusion were analyzed.Combined with the method of spreading spectrum in this paper,it is concluded that no additional compensation is needed.A high-speed level shift circuit is designed to achieve a high switching frequency of the system.A bootstrap circuit is designed to provide a high-side power rail for the upper power MOSFET drive.Innovatively apply segmented controlled technology to optimize the current overshoot caused by the parasitic capacitance discharge of the power MOSFET,thereby optimizing EMI.The influence of the relative position of the power MOSFET on the noise protection of the substrate was studied.This thesis designs a low EMI wide input range BUCK converter with an input range of 3.6V-48 V,a maximum load current of 6A,and a switching frequency between 200 kHz and 2.2MHz.Simulation verification was performed under the 0.18?m 60 V BCD process.The simulation results show that under typical application conditions,the BUCK converter designed in this thesis functions normally and has a good linear regulation and load regulation.Under the condition of high voltage and high duty cycle and light load,the designed bootstrap circuit can achieve the expected goal.The EMI optimization effect of spread spectrum is verified,and the experimental results show that the use of spread spectrum can attenuate 12 dB of noise energy at the switching frequency.The output ripple is simulated and verified,and the output ripple is analyzed.The result matches the conclusion that no compensation is needed.The effect of block driving is verified.The current spike is optimized by 1/3,and the EMI is optimized by 0.51 dB.The overall optimization effect is good,and the EMI optimization effect is 12.61 dB,which achieves the expected goal.