A 7-Cell, Stackable, Li-Ion Monitoring and Active/Passive Balancing IC With In-Built Cell Balancing Switches for Electric and Hybrid Vehicles

Electric vehicles (EVs) and hybrid EVs need stacked lithium-ion (Li-ion) cells to achieve the required high voltage (HV). Cell monitoring and balancing in a stackable battery system is necessary to compensate for accumulative discharge mechanisms and keep the individual cells in the same state of charge. In this article, an integrated circuit consisting of a 12-bit successive approximation register (SAR) analog-to-digital converter is designed to measure, monitor, and balance Li-ion cell voltages with a measured accuracy of $\pm$ 7 mV. These stacked cells are compared simultaneously with a reference voltage to balance the cells. Balancing switches for charging/discharging of the cells are integrated within the circuit to support a balancing current of up to 100 mA, which reduces the number of external components for balancing significantly. The circuit supports both active and passive balancing. A synchronous voltage mode level shifting circuit is implemented for communication between the stacked integrated circuits (ICs) to eliminate external components. Internal linear drop outs (LDOs) (3 and 5 V) power most of the blocks in the IC. The design is fabricated in HV 0.35  $\mu$ m complementary metal oxide semiconductor (CMOS) technology and found to consume a quiescent current of 17  $\mu$ A.