Lithium Battery Charger Design And Research Of The Chip

Li-ion batteries are being widely used, because 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, 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 paper. And different impacts on the performance of battery via different charging ways and process are analyzed in detail, based on which, a charger IC for Li-ion battery is designed.The Li-ion battery IC use CC/CV charging mode which includes the3charging 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 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 is proposed:temperature protection and periodic protection. The overheated 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 of0～40℃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 periodic of the Li battery with certain capacity is assessable, a timer can be added to disable charging if the maximum charging period is exceed.This charger IC adapts the structure of DC-DC with linear charger. Firstly, it converts the input voltage to a specific value above the battery voltage, with which the IC charges the battery then. The advantage of this structure is to combine the advantages of the switch-mode charger and linear charger, taking into account the conversion efficiency and system complexity.Moreover, with the handheld electronic device battery capacity become larger and larger, the dynamic path management (DPM) in the charging process has become increasingly meaningful. Dynamic path management allows the user to run more applications and procedures during the charging process on the device, and not subject to the charger output current limit. Besides, user can program the charging current and the period, so it provides more flexibility. The power MOSFETs are integrated on the die, and the IC is capable of operating correctly only with addition of a few external parts, which demonstrate its high integration level.The circuit was simulated via HSPICE based on CMOS0.5um process, whose results indicate that essential characteristic curves for charging, including:the charging voltage¤t vs. time, the battery voltage vs. temperature&input voltage and charging current vs. temperature, are in perfect agreement with the theoretical analysis and satisfy the design requirements well, which demonstrates the excellent performance of the Li battery charger IC described in this thesis.