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SN74LV4T125: Is 3.3v to 2.8v logic level possible?

Josh L
Prodigy 40 points
Part Number: SN74LV4T125
Other Parts Discussed in Thread: SN74AUP3G34, SN74AXC4T774

Hello,

I am trying to find a part which can shift a 3.3v SPI signal to 2.8v, for an embedded TFT display application. I am struggling to understand whether any of the TI level shifters can output 2.8v, or are they limited to the list of specified voltages in the data sheets... e.g. 1.8v, 2.5v, 3.3v, 5v etc etc. Are these just examples of possible voltages, or if I use a reference voltage of 2.8v will that successfully cause a component such as the SN74LV4T125 to output at 2.8v?

I'm new to this, so apologies if this question is flawed. Be gentle!

Thanks in advance,

Josh

  • 0
    Guru 243870 points

    All logic devices can run with any supply voltage between their specified minimum and maximum.

    For unidirectional downshifting, you can use any buffer with overvoltage-tolerant inputs, i.e., any device in the AHC/ALVC/AUP/LV-A/LVC/LVT families.

    What frequency do you need?

  • 0 in reply to Clemens Ladisch
    Prodigy 40 points

    Thanks for your help!

    I haven't narrowed down the exact frequency, but the minimum serial clock cycle time for the display's SPI interface is 150ns = 6.67mhz. So it will realistically be a lot less than that.

    I'll go down the path of generating a 2.8v voltage and using that to power a level shifter, on the assumption that I'll get 2.8v logic signals out the other side.

    Cheers!

  • 0 in reply to Josh L
    Guru 243870 points

    6 MHz is no problem for any family. Try the SN74AUP3G34.

  • 0 in reply to Clemens Ladisch
    TI__Guru 56070 points

    Thank you, Clemens!

    Josh, you could also consider using the SN74AXC4T774 for level shifting specifically for SPI signals. They are 4 channel device with individual DIR control per channel to be able to level shift 1.8 to 3.3V on 3 channels and 3.3 to 1.8V on 1 channel OR vice-versa as required for the SPI interface.

    Please refer to the app note:

    and the video:

    Let me know if everything works out for you.