Design Of A Lithium-ion Battery Charger IC

Because of their weight, size, useful life and higher available energy densities, lithium-ion batteries have become increasingly popular for use in portable electronic devices. The numerous advantages it are offset by the additional care and diligence required to ensure lithium-ion charging system accuracy and safety. In this paper, the design of a charger for the single cell lithium-ion battery is presented. The final float voltage is 4.2 V and the charge current could be programmed by an external resistor. The maximal programmable current is 800 mA. Fast but safe charging technology for lithium-ion battery is adopted in this design. Demands for charge algorithms easily implemented and low cost hardware are satisfied by this technology. The paper describes the system design of the charger IC based on this technology. When the under voltage lockout conditions are satisfied, the trickle-current charging in advance is used to protect low-voltage batteries. The charge algorithm is constant-current and constant-voltage changing mode as the battery voltage reaches a safe level. Minimum-current constant-voltage terminating is used to control charge precision. Under voltage lockout circuits, charging terminated circuit and recharging circuit are designed to make sure a safe charging process. An internal thermal feedback loop is added to protect the chip from excessive temperature. Design of a novel BiCMOS bandgap voltage reference is described. The reference generates 1.21 V bandap voltages, providing reference voltage for other circuits in this charger IC. The structure and principle of each module also are presented. 0. 6 μm BiCMOS mixture signal model and Spectre tool are used for simulation. The simulation shows that the design meet the requirements and wok well.