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SN74LV4T125: SN74LV4T125

Rohit Bhat
Genius 15975 points
Part Number: SN74LV4T125
Other Parts Discussed in Thread: LMH6881, , SN74LVC1G14, SN74LVC2G14, SN74LVC3G14

Hi team,

Need to level shift a 0V logic 0 reference to -1.25V logic 0 reference for the LMH6881 device SPI working with max 50MHz SCLK frequency. Could you suggest a suitable part number for the same which can do it? Is SN74LV4T125 the right logic level translator?

Best Regards,

Rohit

  • 0
    TI__Guru* 96711 points
    Hi Rohit,
    I understand that you would like a device that will change a logic LOW at 0V to a logic LOW at -1.25V.

    What are the logic HIGH voltages in these two systems?

    What supplies are available?
  • 0 in reply to Emrys Maier
    TI__Genius 15975 points

    Hi Emery’s,

    The high logic state should be level shifted from 3.3V to 2.0V. Similarly, the low logic state should be level shifted from 0V to -1.25V.

    Basically, a 3.3V/0V SPI logic level shifted down to 2.0V/-1.25V. Supplies are currently open for discussion depending upon the level shift operation.

    Best Regards,

    Rohit

  • 0 in reply to Rohit Bhat
    TI__Guru* 96711 points

    This wouldn't be easy with a logic level shifter since they are designed only to adjust the positive voltage, but a comparator would make short work of this.  Just set the reference to somewhere between the input voltages, then connect to the desired output rails.

  • 0 in reply to Emrys Maier
    TI__Genius 15975 points
    Hi Emrys,

    Could you provide a block diagram or schematic for the comparator solution?

    Also, I was looking into the attached e2e thread which you have answered that could do the trick.
    e2e.ti.com/.../605766

    However, I will need at-least three data lines for CS, SCLK and SDI, and if possible for SDIO. Do you have a suitable bi-directional Schmitt trigger such as the SN74LVC1G14 in three or four data lines? Also, a recommendation for a P-MOSFET would be really helpful that is available in a triple.

    Best Regards,
    Rohit
  • 0 in reply to Rohit Bhat
    TI__Guru* 96711 points

    Hi Rohit,

    Schmitt-trigger buffers are not bi-directional.

    Yes, there are multi-channel versions.  Try the SN74LVC2G14 (2x), SN74LVC3G14 (3x), or the SN74LVC14 (6x) ** note that the last one has a different operating voltage range than the others.

    I'm afraid that pFETs aren't something that I support. You'll have to go outside TI for that one.

    I don't support comparators, but they are (generally speaking) pretty simple to understand.  If V+ > V-, the output is the positive rail.  If V+ < V-, the output is the negative rail.

     

    Vref just needs to be somewhere between 0 and 2V, and the same reference can be shared by all comparators.