How to design EMC for EPSRS485 interface?

The EMC design of the RS485 communication interface for EPS needs to balance interference immunity and signal integrity. Design considerations:

1. Common-mode filtering: Connect a common-mode inductor in series on the RS485 lines (A, B), for example, using the CML series. Its impedance must cover the harmonic frequencies corresponding to the data transmission rate to suppress common-mode noise on the bus.

2. Bus termination matching: Install a 120Ω terminating resistor at each end of the bus to suppress signal reflection.

3. Protection devices: Place RS485-specific protection devices near the interface after the common-mode inductor, such as using a dedicated chip with integrated ESD and surge protection, or using a TVS diode (such as SMBJ6.5CA).

4. Isolation design (optional but recommended): For long distances or harsh environments, use an isolated RS485 transceiver module and provide it with isolated power.

5. PCB routing: Rout A and B lines according to differential pair rules (equal length, equal spacing, tight coupling) and keep them away from power lines.

6. Shielding and grounding: Use shielded twisted-pair cable, with the shield grounded at the EPS end.