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AM5718: Restrictions about the Ethernet circuit of AM5718.

Part Number: AM5718

Hi,

Please tell me about the Ethernet circuit of AM5718. Are there any restrictions on the wiring length in the AM5718 → PHY IC → pulse transformer path?

The PHY IC to be used is DP83822IRHB (TI), and the pulse transformer is 7490100110A (WURTH).

I would like to check if there are any restrictions other than the following in the High-Speed Interface Layout Guidelines.
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Differential pair to clock or high-speed periodic signal trace spacing 50 Mils Differential pair to any other signal trace spacing 30 Mils
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Thanks,

Eevee

  • I do not know the maximum wiring length, but should not be any restrictions if good high speed design rules are followed.  If wire lengths are significant, consider placing series resistors for each AM5718/PHY signal NEAR the TRANSMITTER.  Minimize the number of layer changes/vias.  Use quality PCB material with controlled impedance/solid reference plane.

  • Hi, Robert

    If wire lengths are significant, consider placing series resistors for each AM5718/PHY signal NEAR the TRANSMITTER. 

    What does TRANSMITTER indicate? Is it correct to understand that the reason for inserting a series resistor is for impedance matching?

    Use quality PCB material with controlled impedance/solid reference plane.

    What do you mean? I didn't understand what PCB material I should use from the above description.

    Thanks,

    Eevee

  • Yes - series resistors can be place near the signal's source for matching the output impedance of the transmitter/driver with the impedance of the PCB.  This can improve signal quality for longer traces.