Design And Implementation Of High Gain Buck Converter With Dynamic Slope Compensation

Since the wide application of portable electronic devices,the demand for power management integrated circuits in the market continues to increase.Buck-type Buck converters are widely used in communications,computers,and industrial automation.In recent years,the development of semiconductor technology has become more and more vigorous with the appearance of various types of electronic products,and miniaturized products such as portable and wearable devices have penetrated into every aspect of people's lives because of their small size,low power consumption,and high speed.Become an important development direction for electronic devices.Traditional step-down DC-DC convertor has three control mode,current mode,voltage mode and hysteresis mode.Ripple based constant on-time mode belongs to hysteresis mode,and is widely used because of its easy control loop,lack of outer compensation and excellent load regulation and efficiency.There is a compromise for traditional COT mode convertor.On the one hand,use of multi-layer ceramic capacitor decreases the ESR of output capacitor and reduces ripple amplitude,causing potential stability issue and leading to subharmonic oscillation.On the other hand,excessive ripple would decrease the quality factor Q and slow down the system.Meanwhile,valley detect mode applied in COT control brings in DC offset and reducing accuracy of the whole system.Based on this,this paper come up with a novel DC offset cancelling circuit,in which duty cycle info is added in order to adaptively counteract offset in different conditions and effectively improve accuracy.Lacking of error amplifier makes design more simple and improve the transient response speed.and stability is guaranteed at the same time.Also,in terms of the peak current mode control Buck convertor,slope compensation is required for stability concern.In this thesis,discussion on several slope compensation scheme that is widely used is brought up.Based on stability concern in frequency domain,a novel adaptive slope compensation circuit is put forward.It is easily realized,only output voltage is required to generate a slope that is proportional to it,maintaining quality factor of the system Q to an ideal value and avoiding excessive compensation dynamically.Last but not the least,loop stability concern is analyzed for peak current mode control.Regarding to the COT and peak current mode control Buck converters,BCD is used to do simulation and verification.