I'm looking at an example circuit diagram from ST, and it use sa 48F-01GYDXNL part that I can't find anywhere. It's a gigabit ethernet jack with magnetics, and the datasheet shows a circuit looking like:

Magnetics diagram

Link to the datasheet. I'd like to use a different part, but what I want to know is do I have to have the exact same circuit inside the magnetics ? Is any old RJ45 magjack going to work ? Or is it somewhere between the two ?

The one I'd like to use is possible replacement magjack (datasheet here) which appears sufficiently different to cause me to worry they're not functionally the same.


3 Answers 3


You can use the 08621JX143-F just make sure the pins with TRD go toward the phy. The 08621JX143-F has one less center tap pin and some LED's. The frequency response might be a little different, but the overall functionality should comply with IEEE ethernet standards.

  • \$\begingroup\$ Excellent. Thank you for that - puts my mind at rest, now there's only 999 things to worry about instead of 1000 :) \$\endgroup\$ Sep 18, 2019 at 21:00

you can refer any intel ethernet controller datasheets like i219 enter image description here

Basic specifications will be mentioned there

like isolation,OCL,Insertion & Return Losses, Cross talk , EMI features etc.

refer below links for additional information

Why Are Ethernet/RJ45 Sockets Magnetically Coupled?




How important is the number of cores in RJ45 jacks with magnetics



Magjack designs are often paired with various Ethernet PHY chips or NIC chips that have builtin PHY. There can be differences in:

  1. Jack to Phy turns ratio.
  2. Common mode inductance.
  3. LED support.
  4. Mechanical characteristics.

So you have to select carefully.


Now that you included links to the datasheet for both parts I took a look and compared. I am inclined to believe that the Ethernet jack part of the 2nd link will be electrically functional as with your first link. Do be aware that the jack at the second link does also include two USB Type A socket connectors on the same footprints.

  • \$\begingroup\$ Understood - I might try looking for more instances of the Realtek RTL8211F-CG and see what other people have used with it - though "Voltage Spike" (can't figure out how to @ that name) above thinks the 08621JX143-F would actually work. \$\endgroup\$ Sep 18, 2019 at 21:02
  • \$\begingroup\$ @SpacedCowboy You can't @ someone in different comment sections. \$\endgroup\$
    – user103380
    Sep 18, 2019 at 21:06

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