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SN74LVC1G17: Propagation delay

Remi Freiche
Prodigy 70 points
Part Number: SN74LVC1G17
Other Parts Discussed in Thread: SN74AHCT1G14, SN74LVC2G17

Hello,

Currently using the SN74LVC1G17 for a high speed delta sigma transmission, my application requires good synchronisation between data and clock.

My issue is the following: for Vcc = 5V the datasheet state 1.2 < tdp < 5 ns. This means that at each buffer stage I get 3.8 ns of uncertainty. Having few stages in series for both data and clock my uncertainty reaches problematics value.

On what parameter depends the tdp value? Does the (tdp_MAX - tdp_MIN) value get reduces for a fixed 5V supply and a fixed load ? If I measure this value, will it change a lot if I use the exact same circuit but use another SN74LVC1G17 chip?

Same question for the SN74AHCT1G14.

Thank you in advance and best regards,

Rémi Freiche

  • 0
    TI__Guru* 96591 points
    Hi Remi,
    Propagation delay is a function of many variables, including process variation (ie the differences found between one 'batch' of devices and the next). We can only guarantee the values given in the datasheet.

    If your only concern is that the delays are matched within the same system, then I would recommend using a dual buffer instead of a single buffer - the SN74LVC2G17 contains two Schmitt-trigger buffers, and they will have delays within 1ns of each-other (ie max skew of 1ns) given matched load conditions.

    TI also makes low-skew buffers such as those found here: www.ti.com/.../products.html
  • 0 in reply to Emrys Maier
    Prodigy 70 points

    Thank you for your answer.

    Rémi Freiche

  • 0 in reply to Emrys Maier
    Prodigy 70 points
    I could not find the skew value in the datasheet of the SN74LVC2G17. Can you confirm me that I use the value of 1ns for the max skew for the SN74LVC2G17?

    Thank you.
  • 0 in reply to Remi Freiche
    TI__Guru* 96591 points
    Hi Remi,
    Yes, 1ns is the max slew for all logic devices unless it is otherwise listed in the datasheet. In most cases, the skew is much less than that --- every time I've tried to measure it, I've gotten values between 100ps and 300ps.

    As I said before, if this is critical for your design, TI does have guaranteed low slew parts.
  • 0 in reply to Emrys Maier
    Prodigy 70 points

    Thank you, I think the dual buffer could be a solution.

    I looked into the link you gave me for the low slew parts but I could not find anything for 5V ouput logic or mixed 3V3 / 5V logic. Do you have anything ?

  • 0 in reply to Remi Freiche
    TI__Guru* 96591 points
    I'm afraid I don't know - I only support our legacy devices ("Standard Logic"). I would recommend starting a new post using one of a the part numbers from their forum to get input from the high speed folks.

    I know that's it's very odd to have a high speed system operating at 5V. The vast majority of high speed systems today operate between 0.65V and 1.8V -- anything higher is usually differential signalling.