| Switching power supplies are the most important type of power supply chips.They occupy the power supply market for portable applications with efficient voltage conversion performance.Due to the limitation of battery performance,battery power will decrease with the working time.It is necessary to switch the converter from step-down to step-up to use battery power more efficiently.Therefore,the more efficient voltage conversion performance of the buck-boost converter can meet the increasing demand of portable applications,and it has become a key module in most battery-powered systems,effectively prolonging the service life of batteries and achieving higher working efficiency.Therefore,this article takes a series of researches and designs on the buck-boost converter as the research object.The thesis first introduces in detail the topological structures of various classifications of DC-DC converters,and analyzes their basic principles in detail;in-depth analysis of the buck-boost converter and its structural principles;the control mode of the converter and select the control method used in this article accordingly;introduce the basic system power consumption of the converter.Then compare and analyze the different control methods of the converter,and study the stability of the current mode control converter,design a segmented slope compensation circuit for this;design different work for the low load current of the light load state The mode improves the working efficiency of the converter.Finally,a current mode controlled buck-boost converter with multiple operating modes is designed.The chip has a variety of operating modes.When the load current is large,the chip uses peak current mode control in boost mode and valley current mode control in buck mode;when the load current is small,the chip will use the external FCB pin voltage choose different operating modes for the system under the control of the system.There are three modes in the buck mode:forced continuous conduction mode(FCCM),PSM and constant rate DCM mode;there are three in the boost mode:FCCM,burst mode and constant rate DCM mode.The chip contains a phase-locked loop module,which can achieve external synchronization;contains a compensation network to enable the converter to maintain stable operation;a built-in LDO power circuit supplies power to the logic,drive circuit,and protection circuit;includes a segmented slope compensation circuit,which accounts for different corresponding to different sizes of slope compensation signals during duty cycle,a smaller slope signal is generated when the duty cycle is small,and a larger slope signal is generated when the duty cycle is large,to meet the different requirements of the slope compensation current required for different duty cycles,weaken the impact of slope compensation on the load capacity of the converter.The chip circuit is designed based on the 0.35μm BCD process and verified with Cadence software.The results show that the converter can achieve a wide range of output from 0.8V to 34V in a wide input range of 5V to 36V.It only takes 1.25ms to power up the system to stabilize the output voltage and inductor current,and the static power consumption is only 2.4mA under no-load;when the load current changes from 1A to 5A,the output voltage recovers to stability within 0.15ms and changes only 100 mV;simulation results meet design requirements. |
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