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SN74LV1T125: 1.8V to 5V level translation

TISL
Expert 4620 points
Part Number: SN74LV1T125
Other Parts Discussed in Thread: SN74LVC1T45, NE555, TLC555

Dear Support,

My customer uses our SN74LV1T125, but need to apply a 1.8V at the input, instead of 3.3V.

As the Vih is stated at 2.02V, could you tell us if:

- it could have enough margin, under specific conditions, to accept 1.8Vin?

- I didn't find any pin to pin alternative to perform this 1.8V to 5V, do we have?

- should we move to a dual supply level translator, or do you see any other option?

Regards,

  • 0
    Guru 316440 points

    The actual switching threshold is approximately in the middle between VIL and VIH. However, there are no conditions where a VIH smaller than 2 V is guaranteed.

    For this voltage difference, a proper design indeed requires a dual-supply translator.

  • 0 in reply to Clemens Ladisch
    TI__Expert 4620 points

    Considering that it's at the customer own risk to use it with a 1.8V (not guaranteed at all), can we confirm if, by our design rules, it's possible to go down to a 1.8V VIL?

    Regards,

  • 0 in reply to TISL
    Guru 316440 points

    You mean VIH?

    LV1T at 5 V behaves pretty much like AHCT.

    An 1.8 V input signal will be read as high (typically), but the input PMOS transistor will be partially open, which results in a shoot-through current:

    And there is a little bit of hysteresis. It's not as much as with a proper Schmitt-trigger input, but VILH is dangerously high:

    (from SCAA034)

  • 0 in reply to Clemens Ladisch
    TI__Expert 4620 points

    Hi Clemens,

    Thanks for your feedback.

    Yes your right, I meant VIH(min) in fact.

    To give you more details, the 1.8V input signal (A) is just an ON/OFF signal (no specific data rate) and the output (Y) doesn't require any current (just used to bias another IC). The application needs an industrial grade (-40°C to 85°C).

    Would that help to be more confident in the use of an 1.8V signal?

    I can share you the schematic in private if it helps.

    Regards,

  • 0 in reply to TISL
    Guru 316440 points

    I do not know how the thresholds change with temperature. This has to be determined experimentally. And I fear the safety margin is already too small.

  • 0
    TI__Guru 61870 points

    TISL,

    Please consider using the dual supply level translator SN74LVC1T45 which satisfies these conditions for 1.8V <>5V level translation.

    You could also consider 2 channel (LVC2T45) or 8 channel versions (LVC8T245) of this family.

  • 0 in reply to Clemens Ladisch
    Guru 316440 points

    You asked for "any other option", so I should mention that the NE555/‌TLC555 has a very low threshold voltage on its RESET input.