Design And Improvement Of A Linear Li-ion Battery Charger

Due to its smaller size, lighter weight, higher available energy density and longevity, the comprehensive performance of lithium-ion battery is apparently superior to batteries of other kinds. However, these characters require a powerful charging-control chip to ensure the accuracy and safety of the lithium-ion charging system.In this paper, the design of a charger for the single cell lithium-ion battery is presented. The charging voltage of this charger is stablized at 4.2V, and several functions are specifically designed according to the characters of the battery in every charging status so as to charge safely and quickly.This paper describes the design, analysis and further improvement of the charger chip. When the under voltage lockout conditions are met, the trickle-current charging in advance would be used to protect low-voltage batteries. The charge algorithm would shift to the current charging mode to charge quickly as the battery voltage reaches the minimum safty level. Constant-current and constant-voltage charging mode is adopted when the voltage finaly reaches the value set. Minimum-current and constant-voltage terminating is used to realize charging with a high precision so as to fully take advantage of the the battery volume and prevent over-charge. A novel BICMOS bandgap voltage reference is designed to generate a 4.2V bandap voltage as a reference voltage for other circuits. A novel high-accuracy RC oscillator is presented on the basis of analyzing and comparing traditional digital oscillators and based on the general theories. This paper proposes a new structure of comparator multiplexing, which enabled the comparison of four pairs of voltage by one comparator. The structure and theories of each module are also presented. These measures to improve the circuits simplify the structure, decrease power consumption, improved precision and are easy for application.The design of the chip adopted UMC 0.6U₃0V_BCD_V0.1P1A mixture signal model. By simulating all the functions of the modules and the overal circuit with HSPICE, the feasibility of the design is proved.