ASIL-D Compliant Battery Monitoring IC with High Measurement Accuracy and Robust Communication

Abstract

Electric vehicles (EVs) use numerous Li-ion battery cells to obtain the battery pack voltage of hundreds of volts and capacities of tens of kWh. EV battery management systems (BMSs) monitor and control the state-of-charge (SOC) and state-of-health (SOH) of each battery cell to improve energy efficiency and address safety concerns while charging and discharging. To estimate the SOC/SOH from the open-circuit-voltage (OCV) of a battery cell, precise measurements of voltage (VCELL) and temperature (TCELL) are required. In a master-slave architecture, among the various BMS topologies, a slave BMS measures VCELL and TcELL, balances the targeted cells, and communicates with a master BMS that performs SOC/SOH computation and communications with the EV system. The slave BMS typically includes one or more battery monitoring ICs (BMICs) that monitor a group of individual cells. Continuous research and development on the BMIC are resolving the technological challenges of BMS (Fig. 21.6.1) that need to be addressed with the various design techniques. During EV driving, substantial DC and inverter switching currents flow through the batteries. The low frequency (2-20kHz) inverter-induced noise impedes reliable measurements of VCELL and TCELL. The battery current induces common-mode (CM) voltage noise in the communication cables between BMICs, which may lead to communication failures. This paper presents a BMIC with high accuracy in VCELL measurements and voltage measurements (VAUX) of TCELL (voltage accuracy values of 2mV and 0.5mV, respectively) as well as high fault coverage of safety mechanisms to meet the functional safety (FuSa) requirements of ASIL-D, and pass the bulk-current injection (BCI) test of ISO 11452-4 level 4.