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DP83822I: XFMR recommendation and connection.

Motoyasu Hattori
Genius 9275 points
Part Number: DP83822I
Other Parts Discussed in Thread: DP83867IR

Hi,

*1. Transformer (XFMR) specification

DP83867IR only recommends Open circuit Inductance is 320 to 350uH on XFMR specification, but we have never seen this spec on DP83822I/26I.  Could you please let us know the reason why there is no specification on DP838622/25/26I?

*2. Center TAP connection of XFMR

On DP83822I case, center TAP is connected with Analog voltage.  On the other hands, on DP83825/26/DP83867I cases, center TAP is connected with GND through capacitors.  Why is connection different?  

I think this reason is that line driver is different between current mode on DP83822I and voltage mode on others.  Is my understanding correct?

*3. Pros vs. Cons. Related with Mode.

Could you please let us know the pros/cons of line drivers between voltage mode and current mode?

*4. XFMR internal connection.

For all our Ethernet devices (DP83822/25/26/67), we can find the various internal connection of XFMR such as the following.  Is it possible for users to select all type of internal connection which is satisfied with XFMR specification on the datasheet?

Of course, I understand we recommend XFMR whose parts number are described on the datasheet.

Thanks and best regards,
M.HATTORI.

  • +1
    TI__Genius 16726 points

    Hi Hattori,

    Nice to hear from you again. Please find my responses below

    1. Largely because Gigabit (1000Base-T) has a much stricter standard and we've seen the transformer choice have significant impact on waveform.
    2. Your understanding is correct. It is the difference between current and voltage mode drivers.
    3. At a very high level:
      1. Current mode drivers are easier to control output impedance (usually 50 Ω)
      2. Voltage mode drivers use less current.
    4. I'm not sure I understood the question here. As long the transformer meets the specs provided in the data sheet, it can be used with our part.

    Regards,

    Alvaro

  • 0 in reply to Alvaro (Al-vuh-roe) Reyes
    TI__Genius 9275 points

    Alvaro-san,

    Thank you for your comments.

    For No.4 questions, I know the following XFMRs of various internal connections.  Both are recommended for DP83822.

    Are there no issues to select any internal connections of XFMRs which is satisfied with parameter specs on the TI datasheet?

    Please advise us.

    Thanks and best regards,
    M.HATTORI.