| Based on the project of Institute of Electronic CAD, Xidian University,“Theoretical research on the key technique and the design for the power managementICs”, a synchronous high efficiency voltage mode BUCK-BOOST DC-DC converterXD0627is proposed in this paper.According to the theory of BUCK-BOOST converter that output voltage can stepup and down from input voltage, a novel BUCK-BOOST mode is proposed in this paperto achieve smooth transition as the input voltage declines gradually. Then anameliorative mode of PFM mode, called as Burst mode, is proposed to improveconversion efficiency at light load. XD0627operates in Burst mode at light load,consuming only36μA qucesient current. XD0627enters PWM mode at heavy load, inwhich the output ripple is very small and the conversion efficiency can be up to95%.The design and verification of the chip function and critical cell blocks such asbandgap, osillilator, ramp generator and Burst mode detection are based on a0.18μmCMOS process. The simulation results show that chip can get steady outputs from1.2Vto5.5V, and can maximumly load3A current in BUCK mode and2A current inBOOST mode, and that all performances can meet the specifications over an input rangefrom2.5V to5.5V. |
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