How to improve the interference immunity of the HMI CAN bus?

Improving the immunity of the HMI CAN bus and ensuring reliable communication in automotive or industrial noise environments requires a multi-layered design. First, it is recommended to use an isolated CAN transceiver with an isolation voltage of at least 1kV to break ground loops and prevent common-mode voltage damage to the controller. In non-isolated designs, protection must be applied to the CANH and CANL signal lines using dedicated CAN bus protection devices or combinations such as GDT+TVS. Connecting common-mode chokes in series on the signal lines, such as the CMZ3225A-510T, can effectively suppress common-mode noise. The CAN bus terminating resistor (typically 120Ω) should be accurately matched, and its placement should be at the interface of the nodes at both ends of the bus.

During routing, CANH and CANL must be routed as tightly coupled differential pairs, with strict control over impedance and length matching. The CAN interface circuit should be located in a separate area on the PCB, with its ground plane connected to the digital main ground via a single point via a ferrite bead. The connector shield should be grounded. On the power supply side, provide a clean power supply to the CAN transceiver and ensure proper decoupling. On the software side, fully utilize the error detection and retransmission mechanisms inherent in the CAN protocol. For automotive-grade applications, devices compliant with the AEC-Q standard must be selected. By employing Etymotic's isolation, protection, and filtering solutions, combined with stringent design rules, the electromagnetic interference immunity of the CAN bus within the HMI can be significantly improved.