Research And Design Of Integrated On-Chip Buck Converter Based On ASCOOT

With lightweight and miniaturized development of the portable electronic products such as mobile phones and bluetooth headsets,the space on the PCB board is becoming more and more valuable.Among various power chips,the conversion efficiency of inductive DC-DC converters is generally the highest,but the off-chip inductor and load capacitor required occupy a large area of the PCB board,so the integrated on-chip inductive DC-DC converters are of great research value.This paper analyzes the characteristics of existing integrated passive devices and the working principle of inductive DC-DC converters,and then deeply studies the working characteristics and design difficulties of the integrated on-chip inductive DC-DC converters.For this type of converter,the common control strategies are difficult to prevent the inductor current from overcurrent,and have the problems of large ripple and low efficiency under light load.Therefore,this paper proposes a novel Adaptive Semi-Constant On/Off-Time(ASCOOT)control strategy,and designs an integrated on-chip inductive buck converter based on it:1)The buck converter is designed based on the PFM modulation mode,and the switches are given semi-constant on-time.This makes it have a fast response speed and high efficiency under light load.And at the same time it limits the charging time of the inductor to ensure that the inductor current is within the tolerance range.2)A voltage proportional detection module is designed.It detects the input and output voltage,and adjusts the ratio of the on-time of the two switches based on the volt-second balance formula of the inductor.This alleviates the effect of input voltage changes on the maximum load current.3)A load current detection module is designed.It detects the magnitude of the load current non-destructively and adjust the on-time of the switches in proportion.This reduces the output voltage ripple under light load.4)A switching time adjustment module is designed.It contains the core loop of the converter,and receives the information of the above two modules to adjust the on/off-time of the two switches.The converter is designed based on the TSMC 0.13μm CMOS process.The simulation results verify the feasibility of applying the ASCOOT control strategy to the integrated onchip inductive Buck converter.The maximum operating frequency of the converter is 250 MHz.When the input voltage and output voltage of the chip are 2.5V and 1.2V,respectively,the maximum load current is 100 m A.At the same time,the efficiency reaches 62.9% and the Efficiency Enhancement Factor(EEF)reaches +23.7%.