Systematic Desgin Of The Buck Converter With Fast Load Switching Function

As today’s electronic products have become smaller and smarter,the demand for power supplies from electronic devices has also become diversified and complicated.Increasingly complex electronic systems in applications such as consumer electronics,network communications,and automotive electronics are increasingly demanding for power supply performance.Current mode buck converters are particularly suitable for this high performance application environment due to their excellent output current control capability and fast load transient response.This paper deduces the small-signal model of the current mode control during the load transient and proposes a current-mode loop compensation method aiming at the optimation of load transient speed.By designing a constant-bias senseFET current sensing circuit based on sensed current compensation,the current sensing range is extended,also the sensing offset is eliminated,the the sensing speed is accelerated.The proposed current sensor lay the foundation for the implementation of high-frequency current mode Buck converter.In addition,in order to further improve the load transient speed,this paper designs and implements a transient boost circuit based on capacitive charge balance,which greatly accelerates the load transient speed of the constant on time current mode control Buck converter.The design circuit of this paper is based on a 0.18μm BCD process.The loop gain bandwidth of the current sensing circuit is above 750 MHz in all load ranges and the setting time is less than 8ns.It meets the current sensing requirement of a Buck converter operating at 10 MHz switching frequency using a 0.47μH inductor and can meet higher switching frequency demand.After adopting the proposed loop compensation method,the transient speed is improved by more than 10 times of the traditional compensation method.The recovery time under a full load step of 2A is shortened from 250μs to 20μs.After the the transient boost circuit is used,the recovery time of the light to heavy load transient is further shortened to 5μs,which is close to the response speed limit in the existing switching topology and meets the requirement of fast load switching demand.