Research On Topology And Control Scheme Of Hybrid DC-DC Converter

Power management integrated circuit（PMIC）is widely used in communication devices,consumer electronics,automotive electronics,medical instruments and other fields,which is an indispensable module in electronic equipment.Compared with traditional Buck converter,hybrid DC-DC converter based on switching capacitor and switching inductor has become hotspot and difficulty in the field of PMIC,because it can achieve higher power density and higher conversion ratio with high efficiency.In this thesis,innovative research is carried out on the topology and control scheme of hybrid converters,and two hybrid converters suitable for different applications are proposed.Firstly,in view of the low-input and heavy-load efficiency reduction problem faced by traditional Buck converters in portable equipment,this thesis proposes a T4 Dual-Path Step-Down（DPSD）converter suitable for low-voltage applications,and designs the circuit based on 0.18μm BCD（Bipolar CMOS DMOS）process.The input voltage of the T4 DPSD converter is 2.7V to 4.2V,the output voltage is 1.2V,the load current range is0 to 4A,and the switching frequency is 1MHz.Compared with the traditional Buck converter,the T4 DPSD converter can achieve a higher conversion ratio under the same duty cycle,and the average value of the inductor current is reduced to I_LOAD/（1+D）,which greatly reduces the DCR loss of the inductor and effectively improves the efficiency under heavy load.In addition,the charge sharing bootstrap drive circuit effectively improves the efficiency under low input voltage.The simulation results show that the peak efficiency of the T4 DPSD converter is as high as 95.6%,the full-load efficiency is 89.3%,and the full-load efficiency is 6.40%higher than that of the traditional Buck converter.With the help of the wide-swing charge-sharing bootstrap driver circuit,the efficiency of the T4 DPSD converter is still improved by 1.24%when the input voltage is as low as2.7V.Secondly,this thesis proposes a Constant On-Time（COT）-controlled Differential Double Step Down（D~2SD）converter to improve the efficiency and transient performance in high voltage and high conversion ratio applications.In this thesis,the control scheme combining the DLL loop and the valley current mode COT is used to achieve the effect of improving the current sharing effect and the frequency synchronization.The valley current mode COT control D~2SD converter studied in this thesis is designed based on0.18μm BCD process,the input voltage is 12V to 24V,the output voltage is 0.9V to 5V,the maximum load current is 5A,and the switching frequency range is 800k Hz to 2MHz.The simulation results show that compared with the DSD converter,the peak conversion efficiency of the D~2SD converter increases from 91.51%to 92.13%,and the recovery time and undershoot voltage decrease from 10μs and 324m V to 4.5μs and 136m V,respectively.