Study And Low Power Design Of Lithium-ion Battery Management IC

Li-ion battery has been widely used in the late years because of its large energy density, low self-discharge rate and high single cell voltage etc.. Accordingly, battery management IC has been continually modified and developed. Among electronic parameters of battery management IC, study on functions and low power is more impendent and imperative than on others in order to ensure the Li-ion battery's safety and to prolong its life.Presently, low power theories usually can be divided into digital circuit theories and analog circuit ones independently, and in most cases, they are used in real-time embedded system. Based on the power optimization of a mixed-signal single chip system, the low power consumption and protective functions of battery management IC have been researched to meet the application demands of low power and high precision in this paper.As the theoretic foundation of low power, power optimization from design levels of digital circuit has been discussed with emphasis based on the basic power consumption equation. For analog circuit, the basic and practical limitations are analyzed and deduced. Then various low power methods such as weak inversion circuit, current-mode circuit, floating gate technology and bulk-driven technology have been analyzed and compared. In addition, a universal low power design method has been put forward, which not only considers digital and analog power consumption but also extends digital system power management to mixed signal circuit. As aspects of system functional design, application characteristics of battery management IC have been researched in particular, real-time demands such as over-discharge protection, overcharge protection, three classes over-current protection during discharging, abnormal current detection during charging, load short protection, and 0V battery inhibition have been proposed, which are comprehensive and flexible. As aspects of power optimization methods, dynamic power management used in a mixed signal single chip can be discussed from three levels of power model, policy, and implement. Based on application characteristics of battery management IC, a new workload-driven timeout policy of pre-determined shutdown has been proposed, which has been developed from the primary timeout policy. Also, a two-level power management workflow has been presented. The policy has explicit power optimization purpose, furthermore, it can be implemented easily without high extra hardware cost. A criterion of weak inversion MOSFET is introduced, so status of circuit can be controlled effectively in design.At logic and circuit implement level, based on the finite state machine and power state machine, logic control blocks have been designed. For analog circuit, key blocks have been discussed, bias circuits have been stressed, and low power circuit based on weak inversion MOSFET has been put forward. The design of the overcharge comparator, with the most critical precision among analog blocks, has been introduced in detail. Also, Full design of the key blocks of battery management IC has been presented.At layout design level, the layout of the whole chip has been designed; system functions and...