Analysis And Design Of A Buck Convertor With Constant On Time Control Mode

This thesis is to design a DC to DC buck converter which has high efficiency,simple loop control, adjustable output, and fast transient response, etc.The proposed Buck adopts constant on time (COT) control mode, has twodifferent conduction modes, namely, continuous time conduction mode (CCM) anddiscontinuous time conduction mode (DCM), And the selection of the conductionmode depends on the size of the load current, the converter will be adaptedautomatically according to the size of the load current, when the load current is small,the converter works in DCM, otherwise, works in CCM. And when the two modes ofthe converter are switched appropriately, the efficiency of the converter can be alwaysmaintained above85%, in addition to, the converter in DCM is less efficient, and theCCM has high efficiency. Further, compared to the current control mode and voltagecontrol mode, the COT mode make loop control relatively simple, and the converterhas a programmable operation frequency and a very wide input voltage range, theoperation frequency of which can be set by an external resistor and the input voltagerange of which is4.2V~16V, while the output voltage varies from0.805V to13V thatcan be set by external components.Based on the analysis of basic theory of the buck and the description of commonconverter topology, this thesis introduce the constant on time control mode, and thenfocuses on the loop comparator, soft start/stop circuit, and the current modulationmodule.At last, the thesis uses the1μm BCD technology under HSPICE, verifying theloop comparator, soft start/stop circuit, current modulation module and the system.mainly the soft start and soft stop and the current modulation in DCM, as well as theefficiency of the system, linear and load regulation, start up and shut down of thesystem and transient response. The simulation results show that the design of thisthesis achieved the functions and optimized the parameters.