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DP83822I: Transformerless Ethernet for DP83822I to DP83848K

Satoshi
Guru 19625 points
Part Number: DP83822I

Can Transformerless Ethernet normal operation for connecting DP83822 and DP83848?

（DP83822 ~~ capacitor ~~ DP83848）

If yes, please let me know about capacitor value in this case.

※I referenced AN-1519 and below E2E post, both DP83848 is 33nF and both DP83848 is 100nF.

　But I didn't find capacitor value for the condition of one side: DP83822 and other side: DP83848. 

【Additional information】

 ・DP83822 and DP83848 are put the same board and unused cable. (distance is a few cm)

Best regards,

Satoshi

  • 0
    TI__Mastermind 23675 points
    Yes, transformerless can be used. You can use a cap in the range from 33nF to 100nF.
    Please be sure to set the DP83822 line driver to a Class A instead of Class AB.
    Set register 0x404 to 0x4 instead of 0x2.
  • 0 in reply to Ross Pimentel
    Guru 19625 points
    Ross-san

    Thank you for reply,

    Sorry for additional question, please let me know about two points below;
    ①Is there the other condition for DC blocking capacitor?
    　(High frequency, X7R size, etc)
    ②When cable length is too short(a few mm), is there any careful point?

    ※One customer said that;
    　In the past, the same connection by competitor Ether PHY, it was troubled for communication error at short cable length.
    　They are worry about the same result.

    Best regards,
    Satoshi
  • 0 in reply to Satoshi
    TI__Mastermind 23675 points
    Hi Satoshi,

    I recommend an X7R that is an 0402.
    Keep the rating to what you expect the line would experience (i.e. ESD? if so then use a higher rated cap).

    I have not seen an issue with cable length. Some people do cap isolation with stripline connection, which is extremely short (around 5 inch).
    If you are concerned add some stuff options for cap to ground on TD and RD pins. 10 - 30pf is a good stuff value.