Research Design Of Lithium-ion Battery Charger IC

As the development of portable apparatus and secondary built-in battery has been proliferating rapidly in recent years, it is significant and necessary to give a research on design of safe reliable, fast and high efficient charger which is suitable to battery characteristic, able to extend the battery life and in accord with miniaturization of charging unit.In this thesis, the chemic structure, performance and charging method of lithium-ion battery are studied. And different impacts on the performance of battery via different charging ways and process are analyzed in detail, based on which, an linear charger IC for Li-ion battery is designed. Using the constant current/constant voltage algorithm, the charger can deliver up to 1A of programmable charge current. The charging mode includes the three 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 realize the fast charging; finally, the constant voltage charging is adopted to guarantee that the battery is charged to its full capacity. The advantages of this charging algorithm are shorter charging time and higher efficiency. The charger IC monitors the voltage and current in battery to confirm the charging stage.The charger IC discussed in this thesis, is designed to charge single cell lithium-ion batteries. Besides its excellent charging algorithm, both programmable time and programmable current based terminating schemes are available. A bandgap voltage reference and a current reference used in the charger are described, which has such high supply-voltage rejection ratio and good temperature characteristic that guarantees final float voltage accuracy. No external sense resistor or external blocking diode is required for charging due to the internal MOSFET architecture. Thus, the basic charger circuit requires only two external components, which simplifies the application. Internal thermal feedback regulates the charge current to maintain a constant die temperature during high power operation or high ambient temperature conditions. The structure and principle of each circuit module also are presented.The circuit is simulated via HSPICE based on 0.5um N well CMOS process, whose results demonstrate the excellent performance of the Li battery charger IC described in this thesis.