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LSF0108: LSF0108 - is it ok to operate in bi-direction buffer

Jason Dai
Expert 3720 points
Part Number: LSF0108
Other Parts Discussed in Thread: SN74AXC8T245

Hi E2E,

Could LSF0108 operate in bi-directional buffer function even small voltgae transletion between 1.2V and 1.125V?

If not, may we know the specific reason?

Or any more suitable solution can handle this job as bi-directional buffer function?

BR,

Jason

  • 0
    TI__Expert 3720 points
    add one thing that the interface is MDIO.
  • 0 in reply to Jason Dai
    TI__Guru* 97046 points
    The reason why not is that the LSF needs at least 0.8V between the two supplies to operate.

    It is possible to achieve this translation with, for example, a 3.3V supply and a 1.125V supply, however I would not recommend it. The LSF family of translators is much better suited to large voltage changes than small ones -- I would expect such a small voltage change to be problematic.

    I would highly recommend watching the short video series explaining how the LSF series works here: training.ti.com/LogicMinute

    I recommend using a dual supply transceiver for this translation -- this will allow fine tuning of the supply voltages. The SN74AXC8T245 is the best candidate for this translation.
  • 0 in reply to Emrys Maier
    TI__Expert 3720 points

    Hi Emrys,

    Regarding to LSF family, as you mentioned, it needs at least 0.8V between two power supplies tp oprate it. If so, the condition of voltage translation between 1.2V and 1.8V is not allowed which is shown in datasheet at 1st page. Is it correct?

    BR,

    Jason

  • 0 in reply to Jason Dai
    TI__Guru* 97046 points
    Yes and No -- It's not directly possible to do that, however, if you watch the videos I linked, you can see how it's possible to do things like that. It would take far to much time for me to explain the complete operation of the devices here. It should only take a few minutes for you to see how it works in detail via the videos.
  • 0 in reply to Emrys Maier
    TI__Expert 3720 points

    Emrys,

    Regarding to level shift + buffer solution in MDIO interface, customer needs it could be auto direction detect without any pin control. MDIO is bi-directional signal.

    check the datasheet of SN74AXC8T245 that it seems that it needs to control the direction pin for bi-direction signal.

    Any workaround way or more suitbale part there?

    BR,

    Jason

  • 0 in reply to Jason Dai
    TI__Guru* 97046 points
    If that is the case, then the only option is the LSF0108. I would recommend having them get the EVM to test it out -- also, does their system have a supply that's at least 2V?