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LSF0204: Use dual LSF0204 to achieve 0.8V to 1.2V?

daniel
Genius 5095 points
Part Number: LSF0204

Hi Team,

We know LSF0204 can only support Vref_B range from Vref_A +0.8 to 5.5V.

Can we use dual LSF0204 to achieve 0.8V to 1.2V? Please help check if the schematic is workable.

Thanks

  • 0
    TI__Guru* 97046 points

    Hi Daniel,

    This won't work the way you expect.

    It would be better to use the single supply configuration for the LSF0204, as described in this video:

    Essentially, you will set the threshold for 0.8V operation, then use pull-up resistors on each side to set the output voltage level.

  • 0 in reply to Emrys Maier
    Genius 5095 points
    Hi Emrys,
    Thanks for your help.
    It looks LSF0204 can’t support the level transform from 0.8V to 1.2V due to the limitation of this IC spec, right?
    And could you help to suggest the solution that can meet our requirement from 0.8V to 1.2V?

    Thanks
  • 0 in reply to daniel
    TI__Guru* 97046 points
    Hello Daniel,
    As I posted in my previous response, yes, the device can support this translation, however you must use a single supply configuration which requires one supply to be at least 1.65V. It looks like you have a 3.3V rail available, so this shouldn't be a problem at all.

    The video I posted explains in detail how to complete this translation, and is part of a series that explains the part in detail if you have further confusion on how it works.
  • 0 in reply to Emrys Maier
    Genius 5095 points
    Dear Emrys,

    I have seen the video.
    We got single supply configuration, but it requires one supply to be at least 1.65V.
    So we still need two LSF0204 to achieve 0.8V to 1.2V? 0.8V to 3.3V, and 3.3V to 1.2V?

    Thanks
  • 0 in reply to daniel
    TI__Guru* 97046 points

    No, you do not need two LSF0204's, and using 2 will not work.

    Here's a schematic for how to accomplish the translation you require:

  • 0 in reply to Emrys Maier
    Genius 5095 points

    Hi Emrys,

    Many thanks for your help.

    Could you help to double confirm below topology, since Vref_A is set to 0.8V, I think the A ports for data pins should pull high to 0.8V and B port should be 1.2V?

    Or both A and B ports are available for any level?

    Thanks

  • 0 in reply to daniel
    TI__Guru* 97046 points
    A or B can be pulled to either level. You could also pull them up to 5V if you so desired... or any voltage in-between.
  • 0 in reply to Emrys Maier
    Genius 5095 points

    Dear Emrys,

    Please help to check the EN pin level for our application, since we found the EN pin can support maximum voltage is Vref_A.

    But base on this topology, it will up to 3.3V for this pin, it will violate the spec, so please help to double check.

    Thanks

  • 0 in reply to daniel
    TI__Guru* 97046 points

    Hello Daniel,

    The table you have chosen to reference is part of the typical application in the datasheet, and is not part of the spec. Note the disclaimer at the start of the applications section:

    The table you should be referencing is the Recommended Operating Conditions table:

    Here you can see that the voltage at the EN pin can be as high as 5 V.

    The LSF device is one of our most confusing components to design with - that's why we've created the Logic Minute video series explaining it.  If you have not watched those videos, I would highly recommend spending a little time to go through them.  They contain a great deal of useful information and should prevent further confusion.

    training.ti.com/LogicMinute