| Nowadays,with rapid development of technology,electronic product’s volume is getting smaller and smaller,while the function is getting more and more sophisticated.Power supply design,as the guarantee of electricity supply,is facing a great challenge.As the battery capacity has not yet achieved a breakthrough,high efficient and low power consumption power management chips have become key solutions.In order to guarantee the reliability and accuracy of the power management chip,the current sampling loop is extremely critical.In this thesis,research work falls into two parts: current sensing circuit and current sharing technique in paralleled powers.Firstly,basic information of Buck converter is introduced,including the classification,working mode and control mode of the converter.Then based on the analysis of several commonly used current sampling circuits,the DCR current sampling technique is adopted.In DCR current sampling circuit,the current information of the inductance is derived from the voltage drop on equivalent resistance of the inductance.In this way,the key is the acquisition of the exact voltage drop on equivalent resistance.Usually,an RC branch,whose time constant is the same with the inductance branch,is placed in parallel with the inductor.Nevertheless,the time constants are closely related to the parameters of inductance,capacitance and the resistance,it is difficult to match them in practical application.Therefore,a detailed analysis of the time constant mismatch is given in this thesis.A small signal model with time constant mismatch is established,from which the transfer function from control to output is calculated.Then based on the function,the stability judgement is obtained according to the Bode diagram,which guides the direction of circuit optimization.Secondly,parallelled operation of multi-power-converter is popular for high current applications.In order to solve the problem of current mismatch between converters,the essential reason is analyzed from two aspects,no-load output voltage and output resistance in this thesis.Either inequality of the two factors will lead to uneven current between converters.In practical low-power applications,the same power supply modules can be paralleled with same control voltage;but the output resistance depends on application,especially the voltage drop on the cable resistance from power converter output to the load.For this situation,a simple and extensible current sharing method is proposed,and the simulation results verify the current sharing capability.Finally,the chip performance is tested,including the overall regulator function,load step characteristics,current sharing characteristics,and test results show that the chip achieves the expected results. |
