Research And Design Of High Precision Buck Converter With Wide Input Range

In recent years,with the rapid development of communication,Internet of Things and embedded electronics,the demand for high-performance power supply with high reliability and wide application range is increasing.The Buck converter with wide input range can better adapt to the harsh and complex working environment.At the same time,in order to ensure the high quality of power supply,the requirements for the output accuracy of switching power supply are also gradually improved.Among the various control modes of Buck converter,hysteresis control mode and COT（Constant on Time）control mode are suitable for wide input range applications.By analyzing the steady-state characteristics and loop stability of the basic Buck converter,this thesis deeply analyzes the factors affecting the output accuracy of the Buck converter.From the perspectives of linear regulation rate,loop stability and reference voltage accuracy,the key points to improve the output accuracy of Buck converter with wide input voltage range are found,and then a variety of technologies are proposed for these key points.The simulation and test results show that these technologies are effective in improving the accuracy.In this thesis,two monolithic integrated Buck converters with wide input voltage range are designed: the first is hysteresis controlled Buck converter,which contains two control loops: inner current loop and outer voltage loop.The chip adopts burst operation mode,and the voltage outer loop controls the chip to jump periodically between active mode and sleep mode.The inner current loop is enabled in the active mode to control the alternating conduction of the power MOSFETs and control the inductor current within a certain range.The second is the Buck converter controlled by valley current mode COT,and uses phase-locked loop and ACOT（Adaptive Constant on Time）technology to stabilize the switching frequency.The chip forms an inner current loop through valley current feedback to stabilize the inductor current value,and then forms an outer loop through voltage feedback to adjust the output value of inductanor current,so as to stabilize the output voltage.The hysteresis controlled Buck converter designed in this thesis is based on 0.35 μm BCD process.The input voltage range is 6～45V,the fixed output voltage is 5V,and the maximum output current is 100 m A.The chip has passed the verification of pre simulation and post simulation.Under the conditions of full temperature,full process corner,full input voltage range and 100 m A heavy load,the output voltage accuracy of ± 0.8% is achieved.Under normal working conditions,the linear regulation rate of 0.0039% and low load regulation rate are achieved.The COT controlled Buck converter designed in thesis is based on 0.18 μm BCD process.The input voltage range is 6～40V,the output voltage is adjustable,and the maximum output current is 2A.The chip has passed the verification of pre simulation and post simulation,and has been taped out.The finished chip achieves the output voltage accuracy of ± 5% in the full input voltage,output voltage and load range,and has extremely low linear regulation rate and load regulation rate.