What coupling capacitor to use for Single-Pair Ethernet (10Base-T1L)?

The recommended coupling capacitors for 10Base-T1L are 220nF ceramic capacitors for 10Base-T1L Single-Pair Ethernet. You can use X5R or X7R dielectric types. There is nothing special to consider, you can just use standard SMD capacitors.

What voltage rating to use depends on whether you want

• If you don’t use PoDL or you use a isolation transformer with PoDL, using a 10V rated capacitor is sufficient (such as for the TI DP83TD510E-EVM).
• If you use PoDL without isolation transformer, you should use at least a 100V rated capacitor (such as for the TI DP83TD510EVM-PoDL). For the PoDL itself, 63V would be sufficient but that has a low margin for high energy overvoltage events (and surge test according to IEC 61000-4-5).

When using an isolation transformer, ensure to use a Ethernet-rated overvoltage protection diode such as ESD302 on the PHY side of the transformer, before the coupling capacitors. This ensures that EFTs and other high-voltage events are clamped before they reach the PHY.

Sources:

• TI DP83TD510E EVM