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DP83848C magnetics

Kent Suzuki
Prodigy 40 points
Other Parts Discussed in Thread: DP83848C

We’re an engineering consulting firm designing a recording/mixing console for a client.  We’re using the DP83848C PHY chip for this particular 100-BaseTX Ethernet implementation, and while we normally use an Ethernet jack with integrated magnetic that they’ve always used with this IC, we now need to use an EtherCon locking Ethernet jack for this particular high-end-audio console.  These EtherCon (http://www.neutrik.com/en/ethercon/) jacks don’t offer integrated magnetic, so I was wondering if you had a list of approved magnetics to use with the DP83848C. 

The client already has a Pulse H1086NL in their database, but I don’t see any other 100-BaseTX magnetics in their system.  Looking at the H1086NL datasheet, it’s connecting to a TREF pin on the Ethernet PHY.  The DP83848C doesn’t have this pin, does it?

Thanks and best regards,

Kent

  • 0
    Prodigy 40 points

    Here's a follow-up.  One other option the client would like to explore is a standard RJ45 Ethernet jack with integrated magnetics and LED's.  They have such a jack in their database: http://www.belfuse.com/Data/Datasheets/08B0-1X1T-06-F.pdf.  Would this work with the DP83848C?

  • 0 in reply to Kent Suzuki
    TI__Mastermind 31600 points

    Kent,

    The Pulse H1086NL magnetics are asymmetric with respect to the TD+/- and RD+/- paths.  The series choke for the RD+/- path is on the device side of the transformer.  The electrical specifications for the magnetics meet or exceed the magnetics requirements for the DP83848, but due to the asymmetry and location of the series chokes, these magnetics would not be an ideal choice for some applications using the DP83848. 

    The BelFuse magnetics look like a very good choice.  The series chokes are symmetric and on the cable side.  The electrical specifications shown in the 08B0-1X1T-06-F drawing meet or exceed the magnetics requirements for the DP83848. 

    For reference, the magnetics requirements are called out in the Design and Layout Guide for the DP83xxx devices, AN-1469 (Literature Number:  SNLA079C):

    http://www.ti.com/litv/pdf/snla079c

    In Auto-MDIX mode, the DP83848 will swap the TD+/- and RD+/- pins to account for a straight or crossed cable.  For applications using asymmetric magnetics, the device will see a different path based on the configuration that results from Auto-MDIX.  Using symmetric magnetics results in repeatable, symmetric results regardless of which MDI pair resolve as transmit and receive during Auto-MDIX.

    In general, we recommend using components with the series choke on the cable side of the transformer.  The DP83848 draws current from the transformer in order to develop the transmit voltage through the termination resistors.  A series choke on the device side of the magnetics will work against the efforts of the device to draw current from the transformer. 

    Patrick

  • 0 in reply to Patrick OFarrell
    Prodigy 40 points

    Hi Patrick,

    Thank you for a very thorough and clear explanation! 

    Best,

    Kent