Lithium Battery Smart Charger Ic Chip Design Research

Li-ion and Li-polymer battery are being widely used. Their high energy density and long life make them the suitable selection for portable application. Charging management is the essential part in battery management. Safe reliable, fast and high efficient charger guarantees good performance and application of battery. The chemic structure, performance and charging method of Li-ion and Li-polymer battery are studied in this thesis. And different impacts on the performance of battery via different charging ways and process are analyzed in detail, based on which, an intelligent charger IC for Li-ion or Li-polymer battery is designed.The Li-ion or Li-polymer battery IC use CC/CV charging mode which includes the 3 charging stages: the trickle charging, large constant current charging and constant voltage charging. The trickle charging uses small current at the initial of charging cycle to fix and protect the over-discharged battery; after which, the battery will be charged by large constant current to allow the fast charging; finally, the constant voltage charging is adopted to guarantee that the battery is charged to its full capacity. The three phases approach allows shorter charging time and higher efficiency. The battery status detector, which is designed for constantly monitoring the voltage and current in battery to confirm the charging stage, is also discussed in the thesis.The charging process requires strictly control to guarantee the charging safety of the battery. Two charge protection modes are proposed: temperature protection and period protection. The overheating charging will damage the battery and even cause explosion, on contrary, it is difficult to charge the battery to its full capacity at the under temperature condition. As a result, the charging temperature needs to be confined within the range of 0~45℃as the charging will be disabled once the temperature goes beyond this range, which is achieved by temperature protection module. The charging is unable to accomplished if the battery is damaged or removed and IC will always stay at the charging status, fortunately, due to the charging period of the Li battery with certain capacity is assessable, a timer can be added to disable charging if the maximum charging period is exceed.