What is the best topology for adding surge protection to Ethernet PHY?

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Discussion Overview

The discussion revolves around the optimal topology for integrating surge protection into an Ethernet PHY setup, specifically considering the placement of a surge protector relative to a magnetic module (B78476A8135A003) and an RJ45 connector. Participants explore the implications of different configurations on performance and component specifications, as well as the lack of surge or ESD specifications in the magnetic module's datasheet.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant presents two potential topologies for surge protection: placing the surge protector before or after the magnetic module, but is uncertain which is more beneficial.
  • Another participant notes that the application note accompanying the surge protector does not clarify the advantages of either topology.
  • Concerns are raised about the specifications required for the surge protector depending on its placement, with one topology potentially requiring higher specifications, leading to increased cost and size.
  • A different perspective suggests that placing primary transient protection at the RJ45 connector could shunt most transient energy to ground, leaving less energy to couple through the transformer.
  • Participants express a need for more information on surge and ESD specifications for the magnetic module, as the datasheet does not provide this information.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the best topology for surge protection, with multiple competing views on the implications of each configuration remaining unresolved.

Contextual Notes

The discussion highlights limitations in the available documentation for the magnetic module, particularly regarding surge and ESD specifications, which affects decision-making on the topology.

johnkelton
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Hi, Guys I have a B78476A8135A003 Magnetic Module from EPCOS and I want to add a surge protector either on the TJ45 connector side or the Ethernet PHY side. I can't decide which way is more beneficial. Here is the topology:

Ethernet PHY : B78476A8135A003 : Surge Protector (SLVU2.8-4) : RJ45
OR
Ethernet PHY : Surge Protector (SLVU2.8-4) : B78476A8135A003 : RJ45

Also, the datasheet of B78476A8135A003 doesn't talk about its surge or ESD specs. How can I determine those specs?

Thanks
 
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johnkelton said:
Hi, Guys I have a B78476A8135A003 Magnetic Module from EPCOS and I want to add a surge protector either on the TJ45 connector side or the Ethernet PHY side. I can't decide which way is more beneficial. Here is the topology:

Ethernet PHY : B78476A8135A003 : Surge Protector (SLVU2.8-4) : RJ45
OR
Ethernet PHY : Surge Protector (SLVU2.8-4) : B78476A8135A003 : RJ45

Also, the datasheet of B78476A8135A003 doesn't talk about its surge or ESD specs. How can I determine those specs?

Thanks

Welcome to the PF.

Does the Surge Protector not come with some application note?
 
Hi, Thanks for your reply. Yes you are right it did come with the application note. However, the application note is actually the options mentioned above. It does not go into the benefits of either topology over another. I am mainly interested because let's suppose a surge happens, then Magnetic module (1:1 ratio transformer for Tx and Rx) in theory should help diminish the effects of the surge because its composed of couple of inductors. If I add a surge protector component the following way:

Ethernet PHY : B78476A8135A003 : Surge Protector (SLVU2.8-4) : RJ45

then the surge protector components needs to have higher spec which means >$ and >size.
However if the other topology is used then I can lower the spec of the surge protector which will allow me to use small package size (very important for my pcb as I have very little space).

Your thoughts!
 
johnkelton said:
Hi, Thanks for your reply. Yes you are right it did come with the application note. However, the application note is actually the options mentioned above. It does not go into the benefits of either topology over another. I am mainly interested because let's suppose a surge happens, then Magnetic module (1:1 ratio transformer for Tx and Rx) in theory should help diminish the effects of the surge because its composed of couple of inductors. If I add a surge protector component the following way:

Ethernet PHY : B78476A8135A003 : Surge Protector (SLVU2.8-4) : RJ45

then the surge protector components needs to have higher spec which means >$ and >size.
However if the other topology is used then I can lower the spec of the surge protector which will allow me to use small package size (very important for my pcb as I have very little space).

Your thoughts!

Can you give a link to the application note?

I don't work with Ethernet PHYs much, but I do work with other types of communication networks. I usually put the primary transient protection at the network input (your RJ45) before the transformer. Then I put secondary transient protection after the transformer before the transceiver silicon (usually just clamp diodes to the rails). The primary protection shunts most of the transient energy to Earth ground, so only a little is left to couple through the transformer.
 

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