A Wide-Input-Range Buck Converter Design For High Frequency Applications

With the rapid development of communications,automotive electronics,and aerospace,the demand for high-performance power of high-reliability,wide-application is increasing.Buck converters with wide-input and broadband work ability can better adapt to harsh and complex work environments.Through detailed comparison and analysis of two popular control modes in the industry,this thesis finds that the peak current mode outperforms constant on-time(COT)control mode in terms of output accuracy,low EMI characteristics,and noise immunity.So in applications requiring low EMI,high reliability,and with 2A current load,peak current mode is more suitable for wide input range buck converters as a control mode.But the design of an extra light load mode is required because of minimal load limitations and lower light load efficiency in peak current mode.The power loss constitution of the buck converter is analysed in detail.And the highest conduction loss under heavy load should be defined,and the switching frequency and static power consumption should be reduced under light load.to increase the conversion efficiency of the full loadAccording to the above control mode selection and efficiency analysis,the parameter design and layout design of the power tube is completed in this thesis based on 0.35μm BCD process.A high-speed low-power drive circuit is designed,including a pulsed high-voltage level shift circuit,whitch meets the delay time of less than 5ns within the full working voltage,and can effectively reduce the 30%driving power loss.A bootstrap circuit with self-differential detection and built-in undervoltage protection is designed,and the.problem that general bootstrap circuit cannot be recharged under long-term light-load conditions is solved.Dual-light-load mode is designed,including a high-efficiency burst mode and a low-output-ripple skip cycle mode.And a multi-function oscillator is designed with the function of frequency-modulation,frequency-reduction,mode selection and clock synchronization.Considered of the influence of bonding wire parasitic parameters,the system-level simulation of the wide-input buck converter is performed in this thesis.The undershoot voltage and overshoot voltage caused by the load transient response are 160mV,the recovery time is 40μs.And under the condition of 3.3V output,the efficiency is between 63%and 92%,and the dual light-load mode is verified by simulation under ultra-low duty cycle.The application of ultra high frequency 2.4MHz is verified by simulation and functions are normal.All circuits are divided into power modules,digital modules and sensitive modules and layout design is completed.Three schemes are adopted to complete the board-level design with low EMI,including adding EMI filter at the input,adding RC absorption circuit at the SW,reducing the high di/dt loop area.And Six-layer board is used for tracing to reduce noise interference.Finally,a high-reliability,low-EMI,wide-input-range,high-frequency buck converter power module of 15mm × 9mm × 5.5mm is to be completed in a ceramic package.