Research And Design Of External Synchronous High Efficiency Buck-boost Converter

In recent years,with the rapid development of the national integrated circuit industry,it has promoted the advancement of a large number of domestic IC companies.The switching power supply chip industry is also advancing with the times,and various high-quality and high-precision chips are emerging.Based on the buck and boost DC-DC converters,this article designs a buck-boost DC-DC converter chip XD2000 with a wide input voltage range,high efficiency and large load capacity.The buck-boost converter designed in this paper can work in buck mode,boost mode or buck-boost mode.When the input or output voltage changes,its working mode can be changed by itself.Based on the four-switch topology used,a new current mode control method for four-switch buck-boost converter is proposed.By designing a switch conversion circuit to change the signals of the two input terminals of the current PWM comparator,the converter selects different control methods in the buck or boost mode.In boost mode,the converter uses peak current mode control;in buck mode,valley current mode control is used.Taking full advantage of the symmetrical relationship between valley and peak current mode,a frequency-adaptive segmented slope compensation circuit is designed to overcome the subharmonic oscillation phenomenon that occurs under certain duty cycle conditions during peak and valley current mode control.A single slope compensation circuit meets the compensation current requirements in different modes,which greatly reduces the chip area and saves manufacturing costs.CPPLL is designed inside the chip to synchronize the internal operating frequency with the external input clock,which satisfies the multiple parallel use of the chip to provide more current.The external synchronization clock frequency range is 200 KHz ~ 400 KHz.In addition,in order to improve the efficiency under light load conditions,a low current operating mode is added.According to the different voltages connected to the FCB pin,buck and boost can work in three different modes.When the voltage of the FCB pin is less than 0.8V,both the buck and the boost work in the forced continuous conduction mode;when the voltage of the FCB pin is between 0.8V and 4V,the buck works in the skip mode,and the boost works in the burst mode;When the voltage of the FCB pin is between 4V and 5V,both the buck and boost work in a constant frequency discontinuous conduction mode.XD2000 uses 0.35μm BCD process to complete the circuit design work,and uses Spectre simulator on the Cadence platform to perform the overall circuit simulation,and uses the Virtuoso layout tool to complete the layout design work.The simulation results show that: in buck and boost mode,the converter starts normally,the output voltage rises smoothly,and the work is stable after startup;the input voltage step response and load step response are good,the overshoot is small,and the recovery time is short;peak efficiency in buck mode is 96.8%,peak efficiency in boost mode is 98%.The overall conversion efficiency of the chip is high,the response speed is fast,and all indicators meet the design requirements.