Routing gigabit ethernet and TVS's

[Northy]

Hi all,

First time routing gigabit ethernet.
I've got to rout the pairs through this TVS:
https://www.mouser.co.uk/ProductDetail/Wurth-Elektronik/824001?qs=Wn16VcyqZWpXmk0GJ%252BKnhQ==

Has anyone any suggestions on how to do it and keep the pairs impedance matched?
Is it just a case of doing it the best you can?
I'm really trying to keep all the components on the top side only.

Thanks,

G

[T3sl4co1l]

What impedance tolerance and unpaired length can you tolerate?

Tim

[hoebagg]

I've only ever had to measure the characteristic impedance of 10g ethernet through harnesses and connectors using a VNA.
Characteristic impedance of the ethernet harness was 100 ohms +/- 5 in my case.

To minimize losses / reflections you'll want to match the impedance of the cable with the PCB.
You'll need to do some math to figure out trace width, pcb material, copper thickness, other layers (assume 4+ layer board?) and match the pcb impedance with the cable... then you can worry about the TVS diodes

J

[tszaboo]

Hi all,

First time routing gigabit ethernet.
I've got to rout the pairs through this TVS:
https://www.mouser.co.uk/ProductDetail/Wurth-Elektronik/824001?qs=Wn16VcyqZWpXmk0GJ%252BKnhQ==

Has anyone any suggestions on how to do it and keep the pairs impedance matched?
Is it just a case of doing it the best you can?
I'm really trying to keep all the components on the top side only.

Thanks,

G

Wurth has a lot of information on their website about routing their specific components. For ethernet and USB especially. They also released books about it, called the Triology of Magnetics, one of the books deals with Ethernet, including the magnetics, ESD, Surge protection, POE... And with Wuerth, ask the application engineers, they simply have the best support, even for small customers.

[NiHaoMike]

Look at how CAT5 or CAT6 is terminated into a wall connector, turns out 1G and below Ethernet is not picky at all.

[Northy]

Hi all,

The part is:
https://www.microchip.com/wwwproducts/en/KSZ9477
Nothing at all in the datasheet 

Microchip have this app note though:
http://ww1.microchip.com/downloads/en/Appnotes/00002054A.pdf
It states:

• A single differential pair should be routed as close together as possible. Typically, when beginning the impedance
calculation, the smallest trace space (4 - 5 mils) is selected. The trace width is then adjusted to achieve the necessary impedance.
• Differential pairs should be constructed as 100 ohm, controlled impedance pairs.

Thanks,

G