DP83869HM: PHY routing distance requirement

Brendan Toy

Part Number: DP83869HM

Hi,

I have a PHY interface from SOC -> PHY (DP83869HM) -> Magnetics -> RJ45. For each segment of the path, is there a maximum signal distance (i.e. PHY to magnetics distance can be no longer than some value?).

over 2 years ago

0 David Creger over 2 years ago

TI__Mastermind 27122 points

Hi Brendan,

You can follow the guidance given in the following post: https://e2e.ti.com/support/interface-group/interface/f/interface-forum/1163166/dp83826e-trace-length-on-mdi-side-before-after-magnetics?tisearch=e2e-sitesearch&keymatch=phy%20mdi%20trace%20length#

MDI routes from PHY to Magnetic to be less than 3 inches with length difference between differential pair not exceeding 20 mils (budget for whole routing from PHY to connector)
MDI routes from Magnetic to RJ45 not exceeding 1-2 inches.
MII trace length not exceeding 5 inches with skew between them not exceeding 200ps.

But please note there is no "absolute" value for these max distances as there are many variables that come into play. The trace lengths should be made as short as possible.

Thanks,

David

0 Brendan Toy over 2 years ago in reply to David Creger

Prodigy 160 points

Hi David,

Thanks for the quick response. Do you think you could provide more detail on why the trace length constraint is recommended for #1 and #2? Is it a signal integrity issue? EMI/EMC?

Appreciate it!

Brendan

0 David Creger over 2 years ago in reply to Brendan Toy

TI__Mastermind 27122 points

Hi Brendan,

It is both of those reasons, yes. A long trace will suffer from large insertion loss as well as be more vulnerable to coupling signals and EM radiation.

Thanks,

David

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DP83869HM: PHY routing distance requirement