| As the market of portable applications developing constantly, the demand on high efficiency, high reliability becomes the new design challenge to switching power supply IC.First of all, the technology and trend in development of switching power supply is summarized, and the operation theory and basic control mode of the BUCK converters is introduced. Based on them, a synchronous step-down converter operating in Hybrid mode is proposed. Firstly, the whole architecture is put, the working principles and outstanding system performances of the chip are also explained. Secondly, the design procedure of some primary function blocks such as softstart are presented, and validated by Hspice simulation. Finally, providing the typical application circuit as the foundation of the simulations for the whole chip, the results of the simulations prove the feasibility of the aforesaid methods.Based on the analyses of power losses in both PWM and PFM modes, a new architecture is proposed, which can switch from PWM to PFM or vice versa depending on loads, thus providing higher energy-efficiency in full load range. Input voltage feed?forward is used to achieve good line and load regulation. Dynamic voltage positioning is proposed to allow small output ripple of output voltage in PFM mode, give additional headroom for the voltage drop during a load transient from light load to full load and pull the output voltage actively down during a load transient from full load to light load.The simulations for this design are implemented based on the 0.6μm BCD process. The results indicate that the converter has a fast transient response, a good soft start performance, small output ripple and fine efficiency up to 94% in typical application. |
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