| Switching power supply with its features of small size,high conversion efficiency and wide voltage stabilizing range is widely used in various fields,which has a history of more than 50 years.As an important member of the family of switching power supply,DC-DC step-down switching power supply,namely,the Buck converter has been widely used in life,industrial,military and other fields.With advances in technology,the integration density of components in electronic equipment is higher and higher and their function is becoming more and more complex.New demands are set for the characteristics of their power supply chip such as precision of output voltage,ripple amplitude,dynamic response speed,stability and conversion efficiency.Ripple-based constant on-time(RBCOT)Buck converter is widely used in portable electronic equipment owing to its simple structure,good transient response performance and high efficiency under light load condition.In this paper,the background,significance,research history and present situation at home and abroad of RBCOT Buck converter are firstly introduced and analyzed.The traditional control methods,hotspot issues and existing solutions of RBCOT architecture are also analyzed and discussed.Then the working principle of the Buck converter and its three working modes(continuous conduction mode,discontinuous conduction mode,critical conduction mode)are introduced by analysis and theoretical derivation.The working principle,small signal model and stability of the RBCOT Buck converter are explained afterwards.And then,the design method of compensation parameters and the existing ripple compensation circuit are detailedly analyzed.Aiming at the shortcomings of the existing compensation scheme,a novel on-chip ripple compensation scheme is proposed.Based on the describing function(DF)model,the small signal model of proposed compensation scheme is established.And then,the zero-pole location and the influence of compensation parameters on it are analyzed in detail.In addition,the stability criterion as well as the best value of compensation parameters is derived.Simplis simulation results and experimental results verify the system model and derived stability criterion.At last,the compensation circuit at transistor level is built based on the 0.18?m BCD process.Then a RBCOT Buck converter involving the proposed compensation circuit is simulated in Hspice.Simulation results show that this ripple compensation scheme can enhance the system stability without adding any IC peripheral components and solve the harmonic oscillation problem caused by using ceramic capacitors or other capacitors with low equivalent series resistor(ESR)as the output filter capacitors.And the system has good load transient response performance with small output voltage ripple amplitude. |
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