Signal Integrity in Distributed BMS: Reliable SPI and Ethernet Communication for Next-Gen EVs

Distributed battery management systems (BMS) are critical for scaling electric vehicle packs to hundreds of cells, but reliable high-speed communication between modules remains a challenge. Daisy-chained SPI and CAN FD are widely deployed today, while Ethernet is being evaluated for next-generation systems that require higher bandwidth, synchronization, and diagnostics. This paper examines the signal integrity (SI) challenges facing distributed BMS communication, including skew, jitter, crosstalk, and electromagnetic interference (EMI) across PCB traces and wiring harnesses. HyperLynx and SPICE-based simulations are combined with experimental results on a 192-cell test platform to quantify the impact of layout constraints, impedance mismatches, and harness parasitics. Results show that poor SI design can reduce signal margins by more than 18 dB, leading to data corruption and diagnostic failures. Co-design strategies for PCB routing, termination, and shielding are proposed, achieving up to 30% reduction in jitter and error rates under worst-case EMI conditions. By addressing both current SPI-based systems and future Ethernet implementations, this paper provides practical guidelines for engineers developing distributed BMS architectures that meet ISO 26262 functional safety while enabling scalable and reliable next-generation EV platforms.