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DP83867IR - LED_2 and GTX_CLK

Hirotaka Matsumoto
Guru 27585 points
Other Parts Discussed in Thread: DP83867IR

Hi all

Would you mind if we ask DP83867IR?

<Question1>
About LED_2, does it need transistor to drive LED as the datasheet P50?

<Question2>
About GTX_CLK, is it possible receive 3.3V level?
Or, XI/XO pins are at the same level as VDDIO, so it can accept 2.5V level, right? 


Kind regards,

Hirotaka Matsumoto

  • 0
    TI__Mastermind 23675 points
    Hi Matsumoto-san,

    Question #1

    LED_2 does not need a transistor to drive an LED unless you have one of the two conditions:
    1. want to use mode 2 or mode 3 strap
    2. want to use 1.8V VDDIO operation

    Reason #1, if you want to use strap mode 2 or mode 3 on LED_2, you need a voltage divider network to ensure proper strapping, Without the transistor, you will not be able to enter into mode 2 or mode 3. You will only be able to enter mode 1 or mode 4.

    Reason #2, if you want to use the MAC IF at 1.8V VDDIO, the forward bias of the diode is too high and you will not see the LED illuminate. A transistor will allow you to connect to a higher voltage level to accomplish this.



    Question #2

    GTX_CLK needs to be at same voltage level as VDDIO, just like all the other digital pins.

    XI pin is not at the VDDIO level, it is fixed at 1.8V reference. If you use a 2.5V VDDIO or 3.3V VDDIO, you will need to use the clock divider circuit in figure 29.

    Kind regards,
    Ross