Design Of A Switching Lithium-ion Battery Charge Management Chip

With the rapid development of modernization,portable devices have become popular in various fields,and have shown a trend of diversification.Powered batteries as their core are required to move toward smaller space,larger capacity,faster speed of charging and higher stability.Lithium-ion batteries become the first choice for rechargeable batteries due to their advantages of environmental protection,no environmental pollution,low cost,and long life cycle.Therefore,the deep research of the lithium battery charge management chip is an inevitable trend of the era.Aiming at the problems such as the slow charging speed,low efficiency,high power consumption and complicated circuit design in existing lithium battery charge management chips,this paper designs a switching lithium ion battery charge management chip XD8259.The main research results are as follows.1.An overall architecture that shares a bidirectional topology is designed.The chip will share a synchronous buck/boost converter between the output V_OUT and the power switch output pin SW.When the power source charges the battery,it is a buck conversion structure.When the battery supplies power to the load,it is a boost conversion structure.This architecture solved the problem of large area,the layout area of the chip is reduced to2.3*2.7 mm².2.Power path dynamic management function is possessed.The input voltage will supply power to the system load while charging the battery;when the load current is too large,the system will reduce the battery charging current to ensure the load current preferentially because of the input current limit.When the battery charge current decreases to zero and the load current continues to increase,the system will reduce the output voltage to ensure system power.3.Multiple composite control loops charging structure is designed.The chip has multiple loop structures,including the input voltage limit loop,input current limit loop,constant current loop and constant voltage loop.This achieves smooth switching between trickle charging,constant current charging and constant voltage charging,which ensures the high efficiency and stability of the charging process.At the same time,the Type-III compensation network is used to ensure the stability of the loop and the loop model was verified by simulation.4.The main sub-module is designed and verified by simulation.In the bandgap reference module,two triode collector current ratios are set to reduce the influence of the offset voltage from the operational amplifier,thereby improving the bandgap reference accuracy.The simulation results show that the output accuracy is about 2mV.In the charge pump module,two levels of boost are used and the output voltage is stabilized at a fixed value with negative feedback.In the input current limit module,the circuit has a mode selection function to set different input limit currents according to different identified modes.5.Implement chip layout is designed and specifications are verified by test.The input voltage range of the chip is 4.5V to 5.5V;In charge mode,it has 10%constant current accuracy and 1%constant voltage accuracy,and switching frequency is 1.6MHz;In discharge mode,the maximum current can reach 1.5A,switching frequency is 0.8MHz,and its efficiency is up to 93%.The chip XD8259 adopts 0.18um 20V CMOS process and TQFN-28 package.Finally,the chip samples are tested.The results show that the chip's specifications meet the design requirements.