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DP83822I: Magnetics with choke on the side of the PHY

Diego Souza50
Prodigy 130 points
Part Number: DP83822I
Other Parts Discussed in Thread: TLK105, TLK106, TLK105L, TLK106L,

Hello!

Today we use the PHY TL10x/L witch have the following design notes:

- SLLSEB8C - TLK105/TLK106: "Common mode chokes on the device side of the transformer are required."

- SLLSEE3D - TLK105L/TLK106L: "Common mode chokes on the device side of the transformer are required."

- SLVA531A – TLK1XX Design and Layout Guide: "Use magnetics with integrated common-mode choking devices with the choke on the side of the PHY"

Now TI recommends the DP83822I, that no have the explicit note that choke must be in the device side. The recommended transformers on SNLS505A have both options. I would like to know if the choke on the device side it not mandatory on DP83822I, because on beginning of use of TLK10x/L we had ESD problems until slip the transformer and put the choke on the device side.

Best regards,

Diego

  • 0
    TI__Mastermind 23675 points
    Hi Diego,

    There is no CMC requirement for the DP83822I. The issue in the TLK PHYs was resolved in the DP83822I.
    The reason why a CMC was required with the TLK PHYs is because there is a small parasitic path bridging the TD and RD pins when the device is powered-down. If you do not have a CMC, the link pulses from a connected partner can traverse the parasitic path and show up on the receive pins of the link partner. The link partner then sees a false link since the TLK is powered down, but detects 10Mbps link.
  • 0 in reply to Ross Pimentel
    Prodigy 130 points

    Hello Ross,

    Thank you very much. 

    We had ESD problems with choke on the cable side, like loose of packages, resets of device and sometimes the TLK10x was burned when the discharges was applied on the shields of RJ45 connector. We try to improved the EMC performance in many ways, but the best solution was flip the transformer and put the chokes on the phy side.

    What circuit you suggest to have the best EMC solution?

    Best regards,

    Diego

  • 0 in reply to Diego Souza50
    TI__Mastermind 23675 points
    Hi Diego,

    Best approach for EMC is to have TVS protection between PHY and CMC.
    Have a CMC protected by the isolation of the transformer and ensure that the system ground is separated from your chassis ground.
  • 0 in reply to Ross Pimentel
    Prodigy 130 points

    Hi Ross,

    Thank you very much!!!

    Best regards,

    Diego