Design Of A High Efficiency Four-Switch Buck-Boost Converter Drive Controller Chip

Among the various DC-DC converters with step up/step down capability,the Four Switch Buck-Boost converter has the advantages of high power density,high efficiency and low switching voltage,and is widely used in automotive,industrial,portable equipment,etc.Fields.The two main problems faced by the Four Switch Buck-Boost converter are the improvement of efficiency and the smooth switching of multiple modes.It is necessary to design control methods to balance these two points.In this dissertation,the Smooth transition and efficiency improvement of Four Switch Buck-Boost converter are analyzed in detail.A Four Switch Buck-Boost converter system based on NMOS power switch is designed.The drive controller chip is designed based on 0.18 um BCD process.In order to achieve high-efficiency smooth mode switching,the drive controller chip designed in this dissertation implements four-mode control,namely pure buck and pure boost mode and two transition modes.Using pure Buck and pure Boost mode control,the system's switching loss is reduced,and the overall efficiency is improved.Two transition modes are used to enable smooth transition between Buck and Boost modes,and the average inductor current can be small,avoiding an increase in conduction loss.The system uses valley current mode control when operating in Buck mode and peak current mode control in Boost mode.In addition,the control chip uses a constant frequency pulse width(PWM)modulation method to reduce EMI noise.In the design process of the control chip,the loop stability design problem is mainly discussed.The small signal modeling of the system is carried out,the transfer function of the control signal to the output is calculated,and the compensation network is designed based on this.In addition,this dissertation also introduces the design of key modules in the control chip such as bandgap reference circuit,LDO,error amplifier,voltage-current converter,comparator,oscillator,compensation ramp generation circuit,drive circuit and some protection circuits.The dissertation verified the design of the entire converter system by simulation.The designed control chip has a switching frequency of 200 kHz and can operate at a wide input voltage of 4~36V.When the sampling resistance is 10m?,the maximum inductor current is 14.3A.When the input and output voltages are 12 V and the load is 3A.The efficiency is as high as 98%.