Research And Design Of Fully Integrated Buck Converter Based On ACOOT Control

With the continuous development of semiconductor technology,the integration of chips is increasing,and electronic products are also tending to be miniaturized.The fully integrated Buck converter can avoid the use of bulky off-chip passive components,which significantly reduces the cost and prolongs the service life of the battery.This makes the fully integrated converter of very high research value.Because of the high integration of inductors and capacitors,the operating frequency of the converter is as high as tens of megahertz or even hundreds of megahertz.At this time,due to switching losses and reverse inductor current,the efficiency of the system at light load is greatly reduced.In response to the above problems,this thesis adopts an improved PFM strategy—adaptive constant on/off time(ACOOT)control,and designs a fully integrated Buck converter based on ACOOT control:1)The ACOOT control mode is based on the working principle of constant on/off time(COOT)control,and the structure is improved for the defect that it cannot adjust the working time of the switching tube and the rectifier tube.In order to ensure that the system maintains stable output under different input and output voltages,adaptive time control technology is adopted to automatically adjust the ratio of on-time and off-time according to changes in input and output voltages.2)Aiming at the problem of large output ripple when the ACOOT system is under light load,this thesis proposes a load current detection technology,which uses a parallel RC filter circuit to achieve non-destructive current detection,and designs an analog-to-digital conversion circuit to quantify the detection current to precisely control switch tube and rectifier tube.When the load changes,automatically reduces or extends the conduction time of the power tube.3)When the converter works at high frequency,the reverse inductor current will greatly damage the working efficiency.In order to eliminate the influence of the reverse current,this design introduces an additional off-time calibration loop,and fine-tunes the off-time when the rectifier is off in each cycle until the best off-time is reached.Based on the TSMC 65 nm CMOS process,this thesis designs a fully integrated Buck converter.The simulation results verify the feasibility of the ACOOT control strategy.The results show that: in the typical case of input voltage of 2.5V and output voltage of 1.2V,the maximum load reaches 150 m A,the peak conversion efficiency is 73%,and the efficiency enhancement factor(EEF)reaches +34.2%.The conversion efficiency is still 51.1% under the light load of 10 m A.