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DP83826AE: For a non-PoE Ethernet PHY what is the "drive current capability"

SB
Prodigy 20 points

Part Number: DP83826AE

Tool/software:

My question is not specifically about the DP83826AE (I had to include a P/N to post), but about non-POE Ethernet PHYs in general.

This will seem as an unusual question, but my understanding of Ethernet PHY’s is very limited.

For a non-PoE Ethernet PHY what is the "drive current capability" of most Ethernet PHYs?

My understanding is that for a 10BASE-T the voltage levels are +-2.5V. 

The output impedance of Ethernet is 100 ohms, so that gives 25mA = 2.5V/100 ohms

But, 100 meters of CAT5 Ethernet Cable has a resistance of about 10 ohms.  So, the Ethernet PHY must be able to supply at least 250mA = 2.5V/10 ohms to support IEEE 802.3 100 meter standards.  Is that correct?

What over current protection is built into most non-POE Ethernet PHYs?  If you connected all 4 channels to ground would that damage most Ethernet PHYs?

Thanks!

  • 0
    TI__Mastermind 43555 points

    Hello,

    For non-PoE applications, the PHY shall be rated to support drive of 100 Ohm differential load which is supplied by link partner. If this load is present, that is all the PHY needs to drive the appropriate voltages for 10Base-Te or 100Base-Tx.

    There are some protection as dictated by the HBM/CBM model of the MDI which dictates if a significant transient enters the PHY MDI, it would activate and redirect to GND. 

    Sincerely,

    Gerome

  • 0 in reply to Gerome Cacho
    Prodigy 20 points

    Thank you. 

    What happens, if by accident, RX+/RX- & TX+/TX- data lines in the Ethernet Cable are connected to Ground?

  • 0 in reply to SB
    TI__Mastermind 43555 points

    Hello,

    If the data lines are connected to GND, it would sink more current as PHY would attempt to drive the TX line. RX is an input.

    Sincerely,

    Gerome