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Original question:

LSF0204: driving too strong?

LSF0204: When using LSF0204 for SPI interface(3.3<->5V), must it pull up?

Eggsy Pang
Expert 4985 points
Part Number: LSF0204
Other Parts Discussed in Thread: TXS0104E, TXB0104, SN74AHCT1G125, SN74AVC4T774, SN74AHC125

Hi team,

My customer used LSF0204 for SPI  interface(3.3<->5V), must A or B pull up resistance?

Customer don't want to add pull-up resistance due to size. If it don't use pull up resistance, what happen?

Thanks!

  • 0
    Guru 267960 points

    The LSF essentially has open-drain outputs; it requires pull-up resistors to define the voltage level for high signals.

    The TXS0104E has internal pull-up resistors. (But its edge accelerators make it more sensitive to noise, or capacitive load due to long traces/cables.)

  • 0 in reply to Clemens Ladisch
    TI__Expert 4985 points

    Hi Clemens,

    Thanks for your help!

    As you said, TXS0104E make it more sensitive to noise, or capacitive load, so how to deal with it?

    What about TXB0104?

    Thanks!

  • 0 in reply to Eggsy Pang
    Guru 267960 points

    The TXB does not work with large loads, and requires very short traces. But I do not know how your customer's board looks like.

    SPI actually has unidirection signals, so the most robust solution would be a direction-controlled translator with real buffers. I'd recommend the SN74AVC4T774, but that one does not work with 5 V. So you'd need two devices, e.g., SN74AHCT1G125 for shifting one signal up, and SN74AHC125 for shifting three signals down.