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DP83867CR: RX_CTRL strap

Toshiro Imi
Expert 7190 points
Part Number: DP83867CR

Hello,

While our customer studied DP83867CR evaluation module DP83867ERGZ EVM, she had a question RX_CTRL resistor option shown in below. Would you please help her out the reason R21=6.04k-ohm, R23=2.49k-ohm are taken ? Are there any specific reason you choose those number ?

Best regards,

  • 0
    TI__Expert 5425 points

    Hi Imi-san,

    The resistors are not populated so that the user can populate the resistors themselves and set the ANEG_DIS strap setting to either mode 3 or 4. As a result, you will have to populate the straps yourself to either mode. Those values are chosen because they are the recommended resistor values to strap ANEG_DIS to mode 3, which enables the auto-negotiation feature.

    Regards,

    Adrian Kam

  • 0 in reply to Adrian Kam
    TI__Expert 7190 points

    Hi Kam-san,

    Thank you for your help. I understood RX_CTRL must be tied either 6.04k or 2.49k in external. However if this is simple pull up or pull down purpose, the customer think arbitrary resistor value should be allowable. Are there any specific reason you suggest external 6.04k pull up or 2.49k pull down.

    best regards,

  • 0 in reply to Toshiro Imi
    TI__Expert 5425 points

    Hi Imi-san,

    Any resistor values are allowed as long as the target voltage for mode 3 or 4 is met. The target voltage is detailed in section 8.5.1 of the datasheet. We recommend those values specifically because we have tested the device with it. In addition, both the pull up and pull down is necessary since it is a 4-level strap configuration.

    Regards,

    Adrian Kam

  • 0 in reply to Adrian Kam
    TI__Expert 7190 points

    Thank you very much. I understood.

    Best regards,