Design Of Switch-mode Charging Controller For Lithium-ion Battery

In the recent decades, electronic technology developed fast, especially in the customer electronics field, which makes portable electronic products be the development direction. With more functions, faster, smaller, portable battery-operated devices has a demand of longer run time, more lighter and higher efficiency on battery. With the advantages of high energy density, long life time, high discharge voltage, non-polluting and no memory effect, Lithium ion battery is an ideal power supply for portable electronic devices. On the other side, it needs strict requirements such as high precision current and voltage, multi-stage charge and perfect protecting functions in the process of charging. To meet the demand of high precision and segment charge, switch mode battery charge controller based on standard 0.5um CMOS process is presented in this thesis.Firstly, features of Lithium ion battery is introduced, three charging control methods: constant voltage charging, constant current charging and constant current constant voltage charging(CC-CV) are specifically elaborated, and analyses the merits of CC-CV. Then charging control system design is presented, including charging topology, choosing control loop, calculating inductor and output filter capacitor. At last, design and simulation of internal key sub-circuit blocks which are band-gap reference, soft start, under voltage lock out protect, over temperature protect and RC oscillator are elaborated, and the whole chip is simulated to verify and meet the feature spec. This article emphasizes design of high precision current mode band-gap reference and realization of soft start and soft driver.The total layout of charging controller chip IC occupies an area of 3mm×2mm, and chip is taped out in a standard 0.5μm CMOS process, thus earning a low-cost advantage. In this design, the simulation results show that temperature coefficient of band-gap reference with a 1.25 Volt is 13ppm/℃, and the output voltage accuracy is within 0.5% by trimming process variation with trimming circuit while operating temperature ranges from-40 to 120℃. The charging controller’s switching frequency is 1.5MHz with the switch mode charging method achieving high efficiency adopting soft driver technology, at the same time, it has these protecting functions as follows: soft start, under voltage lock out and over temperature protect.