Design Of High-Efficiency Hybrid Dual-Phase Step-Down DC-DC Converters

In recent years,the electronic information industry including Big-data and automotive electronics have developed rapidly,and the demand for Power management chips in foreign and domestic market is increasing accordingly.As a very important part of Power management chips,DC-DC converters face the challenges as low power density and control loop of high complexity.Compared with the traditional Buck converter,the hybrid DC-DC converters based on switched inductor and switched capacitor have significant advantages in efficiency and duty cycle expansion,and then become the research hotspot and difficulty in this field.The topology of Hybrid Dual-phase Step-down converters and corresponding control loop are studied in depth in this thesis.This thesis has proposed and designed two high-efficiency dual-phase step-down converters applicable to different voltage conversion ratios,and the stability and efficiency of the converters under different conversion ratio are optimized.Firstly,this thesis proposes a Differential Double Step-down(D~2SD)converter suitable for high conversion ratio and large output current applications,which has a conversion ratio only half that of Buck,and can achieve dual-phase current balancing by flying capacitor spontaneously.This converter is designed and implemented by 0.18μm BCD(Bipolar CMOS DMOS)process,and the valley current Constant On-time(COT)control and PLL phase-locked loop are adopted to realize the stable operation.Meanwhile,in view of the slow startup speed of PLL loop,this thesis proposes a preliminary circuit to accelerate startup procedure,which reduce the lock-up time of PLL loop significantly.Secondly,this thesis proposes a hybrid step-down topology T2-DSD(Type-ⅡDouble Step-down)converter which is suitable for low voltage conversion ratio and dual-phase current output applications.T2-DSD also can achieve dual-phase current balancing and be well-suited for backlight driving circuits with series connected LEDs.A dual-phase LED driver is designed by 0.18μm BCD process based on T2-DSD topology,which adopts Constant Off-time(CFT)control and Master-Slave control to realize the stable operation of the converter.The input voltage range of T2-DSD driver is 12V～60V,the output voltage is between 9V～60V,the output current range reaches 3A per-phase,the switching frequency is externally adjustable and its adjustment range is 1MHz～2MHz with PWM dimming function.The simulation results show that the proposed LED driver can quickly restore the steady state during PWM dimming while remaining dual-phase current balancing.Compared with the LED driver based on dual-phase Buck converter,the peak efficiency of T2-DSD converter is enhanced from 96.49%to 98.46%,and the maximum efficiency improvement of 4.52 percentage points at 500m A load is achieved.