How to filter and shield the Ethernet of a frequency converter

Filtering and shielding the inverter's Ethernet interface are crucial for ensuring network stability and data accuracy in industrial environments. Design considerations include: using RJ45 connectors with integrated common-mode chokes and metal shielding, which simplifies design and improves performance. The network transformer is critical; a model with a center tap should be selected. This tap connects to the chassis ground via a high-voltage capacitor, such as a 1000pF/2kV Y capacitor, providing a discharge path for common-mode noise. A common-mode choke, such as the CMZ2012A-900T, can be connected in series on the differential lines between the transformer and the PHY chip to further suppress common-mode noise.

The PHY chip's power supply must be extremely clean, using ferrite beads, such as the PBZ1608 series, and multi-stage decoupling with MLCCs of various capacitance values. In terms of PCB layout, the Ethernet interface area should be relatively independent, with differential connections strictly controlled to 100Ω impedance and traces of equal length and spacing. The ground plane of the interface circuit should be connected to the digital main ground at a single point via a ferrite bead. For applications requiring surge protection, a ground-to-ground (GDT) circuit can be added between the external line and ground of the transformer. By employing high-performance common-mode chokes, filter beads, and protection devices from Eintratronics, Ethernet interfaces can meet industrial EMC requirements.