Research On Modeling And Optimization Design Of Constant-on-time DC-DC Buck Converter

In order to guarantee portable electronic devices working efficiently and reliably,the voltage regulation module should work with fast transient response and high light-load efficiency.Constant-on-time?COT?control,which is a kind of PFM control technique,has advantages of fast transient response speed and high efficiency and is widely used in point-of-load converters and voltage regulators.But there are some problems in the system stability and switching frequency range of COT control.The accurate small-signal model plays an important role in studying the stability of DC-DC converter.In the previous literature,the modeling and stability analysis of COT-controlled Buck converter is conducted under resistive load.In this paper,based on the description function method,a small signal model of current mode COT control and ripple-based COT control Buck converter under current source load is established,and the model is accurate up to the frequency of 1/(2T_CLK).Then,the current source load model is compared with the the resistive load model.Based on the derived model,the design schemes of the stability of COT control Buck converter are discussed.PLL-based frequency locking technology has many advantages in solving the wide range of the switching frequency of the DC-DC converter.But an inappropriate PLL loop design will result in duty cycle jitter,higher output voltage ripple,and even cause the lost tracking to the reference frequency,and eventually lose all the benefits of using the PLL loop,but this problem has not been systematic studied in the previous literature.Therefore,in this paper,a small signal model of PLL in CCM mode and DCM mode is established based on the description function method.The stability problem caused by parameter change is studied in PLL-based COT control converters.And based on the derived model,an adaptive bandwidth phase-locked loop structure is verified.