Support on SLVU2.8‑8A1

[DixitRohit]

Hi,

We are using the ST Micro Devices SLVU2.8‑8A1 TVS array on the primary side of the Ethernet connector for ESD protection in a 1000BASE‑T Ethernet design.

It is observed that when the SLVU2.8‑8A1 is mounted, the 1G Ethernet link reports FCS errors with ~100-metre cables, whilst shorter-length cables work error-free.

When the device is removed, the Ethernet link becomes fully stable and error‑free on the same hardware with longer length cables.

Ideally the device should not interact with the Ethernet data being transmitted. Please check how the device can interact with normal datalink propagation. The problem is observed in designs with PHYs from two leading manufacturers.

Attaching the images of the device as well.

Thanks & Regards,
Rohit Dixit

[Peter BENSCH]

Welcome @DixitRohit, to the community!

The observed behavior is consistent with additional capacitive loading introduced by the SLVU2.8-8A1 TVS array.
Although the device is intended to be transparent to normal Ethernet operation, its parasitic capacitance can slightly affect signal integrity on 1000BASE‑T links, especially on long cables where the channel margin is already limited.

At around 100m cable length, the link is operating close to the specification limits, so even a small additional loading effect may lead to FCS errors. With shorter cables, the available margin is higher and the link remains error-free.

I'd recommend checking:

• the effective capacitance of the protection device in the actual circuit
• the PCB layout around the connector and TVS
• the overall link margin using the intended PHY and transformer design

Regards
/Peter

[DixitRohit]

Hi Peter,
Thanks for the guidance. We will review your recommendations and update you with our findings.

We also want to share an observation: when we evaluated an alternate vendor TVS array (capacitance specified around 2.6 pF typ to 3 pF max per line), we see no FCS errors on the same hardware setup.

Given that, could the 1000BASE-T margin really be that sensitive to small parasitic differences? Or are there other device parameters that could explain why one TVS affects the link while another does not?

Regards,
Rohit Dixit

[Peter BENSCH]

I cannot make a comparison with a device from another manufacturer. However, since we are talking about a borderline case in the transmission distance length, the personal Online Support team may be able to conduct a detailed simulation of both devices with you and analyse the behaviour.

Regards
/Peter