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SN74AVC20T245: Propagation Delay of signal groups / individual signals

Martin M.
Prodigy 170 points
Part Number: SN74AVC20T245

Hi all,

I'm working on a project where we need to level shift a 19-bit wide bus. The propagation delays are very important for the further processing of the data. For the device minimal and maximal propagation times are given in the datasheet for different VCCA/VCCB combinations. Here the questions:

On this device we have two 10-bit "groups". Is the propagation time for both groups the same or does every 8-bit group have a different propagation time inside the given tolerance in the datasheet?

Is the propagation time for all signals within a group  the same or are there differences? If there are differences, how big is time skew?

Thank you an best regards,

Martin

  • 0
    TI__Guru* 96947 points
    Hi Martin, and welcome to the forums!

    I have to start by saying that this device wasn't characterized for skew, so I don't have data to refer to and I can't guarantee anything.

    To answer your question -- any logic device like this is designed to make all the channels the same. There will be very minor fluctuations due to the manufacturing process, however these are not what creates the large range shown in the datasheet. The datasheet timing ranges are given to account for temperature and process variation. It is very reasonable to expect all channels to be very close to one another within the same chip since all channels are subjected to the same conditions.

    The best chance for good skew numbers in a simple logic device (like the SN74AVC20T245) is to use a single IC for the entire bus. Process variations across a single IC will be minimal, typically results in skew under 1ns. If more than one IC is used, the variation can be much larger.

    As long as the loads are equal and the system is tolerant to ~2ns of skew between channels, I don't think you will have any problems.
  • 0 in reply to Emrys Maier
    Prodigy 170 points
    Hi Emrys, thank you, your answer was very helpful!