Design And Implementation Of A Step-down Lithium Battery Charging Chip

With the progress of society and the continuous development of economy,all kinds of electronic products account for an increasing proportion in people’s lives.In particular,the demand for portable electronic products such as mobile phones,tablet computers and wearable electronic devices is growing explosively.As the energy supply unit of these devices,lithium-ion batteries are also widely used.The cycle life of lithium battery is seriously affected by its charging mode,even unreasonable charging mode will make the battery spontaneous combustion.Therefore,as the management of its charging process,charging chip also ushered in vigorous development.In this article,a novel buck switching lithium battery charging chip is designed and implemented.The chip can only charge a single battery.Its switching frequency is660 KHz,its constant current charging current can be adjusted freely in the programming range of 0.4A to 2A,and its constant voltage charging voltage is 4.2V±0.035 v,the recharge voltage is 4V,the charging efficiency is up to 90%,support 2.2μH small inductor work,support the maximum charging time limit,battery temperature protection,input under/over voltage protection,chip over temperature protection and charging state indication and other functions.The whole process of chip development can be roughly divided into: firstly,the architecture of the whole chip system is determined according to the market and my research direction;Then,the design and simulation of each sub circuit module and the whole system circuit are completed in cadence;Next,the related layout design and rule verification are completed in 0.18μM Bi CMOS process;Finally,the function and performance of the chip are tested.In order to get the enough highly performance chip and enough highly market recognition,this article makes the following innovations:1.In order to make the chip charge safely and effectively in various input environments.In this article,a unique input adaptive loop is designed to keep the output stable at 4.3v when the load capacity of the input power supply is weak,and a unique multi loop smooth switching system is designed to realize the safe and smooth switching between the loop and the traditional constant current charging loop and constant voltage charging loop.This technology solves the problems of high cost and high circuit complexity of using additional chips or ADC(analog to digital converter)to sample and control charging current.2.In order to achieve ultra-low supply voltage charging as low as 4.3v.In this article,a unique constant off time control mode is adopted to make the system work at approximately 100% duty cycle.3.In order to reduce the cost of the chip and realize zero power consumption of the battery without adapter.In this article,a unique substrate switching technology is used for real-time substrate management of power PMOS.This technology successfully uses a single PMOS instead of two series NMOS power transistors to complete the effective isolation between the adapter end and the battery end.The application of this technology can reduce the area of power devices by nearly 20%.4.In order to get sufficient and better loop stability,this article uses MATLAB to simulate the loop transfer function in frequency domain and load transient step response to verify the loop stability.