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DP83TD510E-EVM: DP83TD510E: Resistors of the Termination Circuit in DP83TD510E-EVM

Gerrit Telkamp
Prodigy 190 points
Part Number: DP83TD510E-EVM
Other Parts Discussed in Thread: DP83TD510E,

The termination network of the evaluation board DP83TD510E-EVM is designed as described in the data sheet DP83TD510E, chapter 8.2.1.3 (Termination Circuit for Non-Intrinsic Safe Applications): The differential output signal TX+/TX- is fed out via R14/R128 with 49.9R each, and fed back via R19/R124 with 2.0k into the inputs RX+/RX- (see chapter 6.4 Analog Front End Schematic of the DP83TD510E-EVM User’s Guide).



I cannot understand why large 1W resistors in 2512 packages were used for R19/R124 (RX). According to the data sheet, the current consumption of RX+/RX- should not exceed 15uA... Do you have any idea why 1W resistors were used here?

  • 0
    TI__Mastermind 25715 points

    Hi Gerrit,

    We will discuss within the team and get back to you later this week.

    --

    Regards,

    Hillman Lin

  • 0 in reply to Hillman Lin
    TI__Mastermind 25715 points

    Hi Gerrit,

    R14, R19, R17, and C118 are all design internally within PHY for other PHY products. R19 and R124 is used for high power dissipation to release the heat during communication. Therefore 1W resistor with large package size are required. Further detail I cannot share it externally.

    --

    Sincerely,

    Hillman Lin

  • 0 in reply to Hillman Lin
    Prodigy 190 points

    Hi Hillman,

    thank you very much for your reply, even if it does not really answer my question. Of course, larger resistors will dissipate more power, but I cannot understand why a greater power could be generated at this point (the RX inputs will have max. 15uA).

    Would it be possible to get more information when signing a NDA?

    Best regards,

    Gerrit.

  • 0 in reply to Gerrit Telkamp
    TI__Mastermind 25715 points

    Hi Gerrit,

    DP83TD510 Datasheet session 8.2.1 regarding to the intrinsic safety might help you with your concern on why we need a high power dissipation tolerance resistors.

    --

    Regards,

    Hillman Lin

  • 0 in reply to Hillman Lin
    Prodigy 190 points

    Hi Hilman,

    I assume that you are referring to this version of the DP83TD510E datasheet: SNLS656C – AUGUST 2020 – REVISED DECEMBER 2020

    In chapter 8.2.1, I find something about the resistance (RRX1=RRX2=2k, RTX1=RTX2=50R). I see nothing about the max. power dissipation. Or have I missed something?

    Additionally, when I take a look at the schematic for the EVAL-ADIN1110, I find a very similar termination circuit. But with RRX1=RRX2=5k1 in a 0603 package with max. 63mW (in contrast to 2k/1W for the DP83TD510E-EVM). Of course, the components might differ in details, but I can't think of any sensible reason why the TI component could generate so much power loss via the input resistance...

  • 0 in reply to Gerrit Telkamp
    TI__Mastermind 25715 points

    Hi Gerrit.

    We will discuss internally within team and we will let you know about it later this week.

    --

    Regards,

    Hillman Lin

  • 0 in reply to Hillman Lin
    TI__Mastermind 25715 points

    Hi Gerrit,

    Sorry, we are still waiting from response internally. We will get back to you as soon as possible.

    --

    Sincerely,

    Hillman Lin