DP83848I: Recommendation for Remoting RJ45 from Ethernet MAC

Emma Yanakiev

Part Number: DP83848I

Hi,

I have a 100Mbps PoE application which requires the RJ45 connecter to be on a separate board from the SoC where the MAC is integrated. We have an FFC connector between the two boards. We are trying to determine the best way to distribute the RJ45/Magnetics/PHY and MAC. Based on what I've found so far, it seems like routing the RMII signals over the impedance-controlled FFC cable is the best option. Do you have any recommendations for this application?

Thanks!

Emma

over 2 years ago

0 Gerome Cacho over 2 years ago

TI__Mastermind 31755 points

Hello,

We have not characterized the PHY to work in this specific manner with ribbon cables, so it is your responsibility to validate the design. However, we do see potential issues (some of which you have pointed out):

- RMII is a 50MHz communication and timing will be very strict as is. Ensure that RMII traces and cables are length matched.

- With ribbon cable, there is inherent signal integrity and EMC risk, so please validate this design accordingly.

Sincerely,

Gerome

0 Emma Yanakiev over 2 years ago in reply to Gerome Cacho

Prodigy 80 points

Hi Gerome, thanks for your feedback. In your opinion, would trying to connect through the MDI signals though cable be even riskier?

0 Gerome Cacho over 2 years ago in reply to Emma Yanakiev

TI__Mastermind 31755 points

Hi Emma,

MDI signals are usually connected via RJ-45 cable to the PHY's link partner. What alternative solution are you proposing?

Sincerely,

Gerome

0 Emma Yanakiev over 2 years ago in reply to Gerome Cacho

Prodigy 80 points

Hi Gerome, I was referring the the signals between the magnetics and PHY. Would it be better to have a board-to-board FFC connection for those signals or the RMII signals?

0 Gerome Cacho over 2 years ago in reply to Emma Yanakiev

TI__Mastermind 31755 points

Hi Emma,

Ideally, there should be direct copper connection on the RMII-to-PHY and MDI-to-PHY signals as opposed to ribbon cable.

Also please note, I will be out of office for the rest of the week, and any subsequent followups will be replied to by next week maximum.

Sincerely,

Gerome

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DP83848I: Recommendation for Remoting RJ45 from Ethernet MAC