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  • TI Thinks Resolved

TXB0108: Not driving the output to 0v INSTEAD it is 1v.

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Replies: 9

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Part Number: TXB0108

Hi,

We are not able to see the TXB driving the output signal to 0v. Instead it is 1v. Attached file has the design information as well as waveforms.

Your help is highly appreciated, please let me know if you need any other information.

Thanks,

Vivek V

  • In reply to Vivek V41:

    Hello Vivek,

    The problem is the RPU you are using.

    Here are some app notes you should read which will guide you on which pullup resistor values you should use and what impact they create.




    Thanks!
    -Karan

  • In reply to Karan Kotadia:

    Hi Karan,

    I tested even by removing pullups on both the side of the level shifter on one of the lines. Still the problem persists

    Thanks

    Vivek V

  • In reply to Vivek V41:

    Hello Vivek,

    What device are you trying to drive with the TXB? Does the device has CMOS inputs? Does the device have internal pull up resistors? The TXB can sink 20uA of current when driving low and any more current will cause the VOL to be as high as you are mentioning.

    Thanks!
    -Karan
  • In reply to Karan Kotadia:

    Hello Karan,

    The device driving TXB chip is our own internal ASIC which has CMOS pins. To be precise we are interfacing it with QSPI Pins .

    Can you please direct me to the specification related to the sink current 20uA you are referring?

     Thanks,

    Vivek V

  • In reply to Vivek V41:

    Hello Vivek,

    If you look at the VOL specs in the Electrical Characteristics table of the datasheet. You will see that at an IOL of 20uA, VOL is .4V.
    So we spec the TXB devices to be only able to drive 20uA of current. It can be a bit more than that but with it the VOL value will rise and just as in your case we see something like 1V VOL instead of less than .4V as it should be.

    Thanks!
    -Karan
  • In reply to Karan Kotadia:

    Hi Karan,

    I understand it now and appreciate your prompt responses.

    Will it be okay to use TXS0108EPWR? From the data sheet I see the IOL as 200uA and VOL as 0.5v. The 0.5V should be good enough to be recognized as logic 0.

    If yes, will you be able to get us some sample part to India?

    Thanks,

    Vivek V

  • In reply to Vivek V41:

    Hello Vivek,

    Here is an FAQ that shows the differences in the auto-bidirectional families. e2e.ti.com/.../719537
    The TXS devices are meant for passive translation and they have no drive. They are also meant for open drain translation and come with built in pullup resistors. Make sure to read the following on using external pullups with the TXS: www.ti.com/.../scea054a.pdf to make sure that your driving device will have enough current sinking capability for the TXS device.

    As for ordering samples, you can do that through the ti store. E2E is for helping customers with technical problems.

    Thanks!
    -Karan
  • In reply to Karan Kotadia:

    Thank you Karan

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