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TXB0106: Problem with signal distortion

Nenad Jovanovic
Prodigy 30 points
Part Number: TXB0106
Other Parts Discussed in Thread: SN74LVC8T245, SN74LVC1T45, SN74LV4T125, SN74LV1T34

Hello Support Team

I have a need for a 6 - bit high speed bidirectional voltage translator. On one side, I have a CPU powered with 3.3 V, and on the other side is a target device with adjustable power 3.3V or  5V. I tried using TXB0106 but there is a signal distortion. Please see attached pictures, CPU on A side of translator is sending a 500 kHz signal, on both sides VCC is 3.3V, C1  is A1 pin  and C2 is B1 pin of TXB0106, PIC1 are signals without target connected (looks good) and PIC2 are signals with target connected (there is a distortion in signal on B side). Can you tell me what is causing signal distortion?

Can you please recommend some of your other devices suitable for this kind of a design? There can not be any pull-up on the data lines, possible pull-down resistors.

Thank you,

Kind regards,

Nenad Jovanovic



  • 0
    TI__Guru 61910 points
    Hi Nenad,

    Please refer to the app note on external pulldown / pullup on the TXB devices. It looks like the external pulldown combined with the capacitive loading is causing the signal integrity issues here.
    www.ti.com/.../scea054a.pdf

    I would recommend switching to direction controlled transceiver like the SN74LVC8T245 for the 3.3 to 5V support.
    Let me know.
  • 0 in reply to ShreyasRao
    Prodigy 30 points
    Hi Shreyas,

    Thank you, I think your answer is right for the TXB0106 problem.
    Thank you for your suggestion, we actually have a working solution with SN74LVC1T45, we are trying to avoid using direction control.
    In this application we need separate direction control for every signal, which is a lot more MCU pins we need to use.
  • 0 in reply to Nenad Jovanovic
    TI__Guru 61910 points
    Hi Nenad,

    I understand. You could also consider using the SN74LV1T34 or the SN74LV4T125 devices which are unidirectional TTL input compatible devices without any DIR control.

    Would you prefer to have the device like the SN74LVC1T45, or LVC2T45 without any DIR control but with preconfigured direction control on the IO channels? I can let the team know about this. What would be the annual appx. production volume?
  • 0 in reply to ShreyasRao
    Prodigy 30 points
    Hi Shreyas,

    Thank you for your suggestion.
    For some data lines we can set fixed direction, so we can use LVC1T45 or LVC2T45 "without DIR control", but we will definitely need few bidirectional lines, so we need a bidirectional solution. We need translation for several of our product lines, so depending on number of channels we will definitely need a lot of translators...