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TLK105 Near-End Loopback

Hubert Zimmermann
Prodigy 30 points
Other Parts Discussed in Thread: TLK105

Hi there,

i want to test the tlk105 with an analog loopback. By the datasheet it is recommended to "attach 100 Ohm terminations to the RJ45". So where exactly do i have to place them in the circuit?

The tlk105 is connected as shown in the datasheet (3.2.1 Single Supply Operation).

Thanks,

H.

  • 0
    TI__Mastermind 31600 points

    Hubert,

    We will provide you with clarification on this test mode shortly.

    Patrick

  • 0
    TI__Mastermind 23675 points

    Hi Hubert,

    Here is a simple diagram to help you visualize the connections you need to make. You should add 100ohm termination between pins 1&2 and also between pins 3&6. 

    Regards,

    Ross

  • 0 in reply to Ross Pimentel
    Prodigy 30 points

    Hi,

    thanks for the fast answer.

    I give you just a quick information, what i want to do:

    I want to use the analog loopback test in-circuit. It must not be an external loopback. In the datasheet in figure 3-5 it shows the analog loopback. It's not written there, between which signal lines i have to place the 100Ohm exactly. That's what i want to know. What signals are pin1/2/3/6?

    Greetings!

    H.

  • 0 in reply to Hubert Zimmermann
    TI__Mastermind 23675 points

    Hi Hubert,

    For analog loopback:

    You want to place one 100Ohm resistor between TX+ and TX-.

    You want to place one 100Ohm resistor between RX+ and RX-.

    Here is an image of the cable you should make for analog loopback.

    As you can see....a 100Ohm resistor is connected between pin 1 and pin 2 and another 100Ohm resistor is connected between pin 3 and pin 6.

    Regards,

    Ross

  • 0 in reply to Ross Pimentel
    Prodigy 30 points

    Hi Ross,

    thanks for your patience.

    This part is clear, but the picture above represent the "external loopback" like in figure 3-5. , right?

    Cause what i want to do is an "analog loopack" without plugging in a cable. Due to the picture it seems possible? Or do i have to plug in the modified cable for both, external and analog loopback?

    Regards,

    Hubert

  • 0 in reply to Hubert Zimmermann
    TI__Mastermind 23675 points

    Hi Hubert,

    No worries at all. Answers to your questions:

    No, the pictures above represents the cable that is recommended for proper operation with analog loopback I can see why with is confusing since there are two loopbacks that require different cables.

    1. Analog loopback needs a termination cable seen above for proper operation.

    2. External loopback needs a loopback cable pictured in Figure 3-5 of the datasheet.

    The two cables are completely different. Analog loopback has 100 Ohm terminations at the end and connects as pictured above. External loopback is a direct connection from pin #1 to pin #3 and from pin #2 to pin #6.

    Regards,

    Ross