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SN74AVC4T774: Datasheet questions

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Replies: 5

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Part Number: SN74AVC4T774

Hi Team,

Would you advise my customer's Switching characteristics question.

My customer is looking for a low latency device to level convert from FPGA 1.8V output to 3.3V.

Frequency range is from 24Hz to 148.5MHz including clock signal.

Q1, She have designed with reference to datasheet rev.E which describes TPLH,TPHL=0.2ns (min) to 2.9ns(max)

    However the latest datasheet rev.F is changed to TPLH,TPHL=0.4ns (min) to 3.4ns(max) at 

    ( VCCA=3.3V, VCCB=1.8V, B → A  case)

    Are there any method to get rev.E spec device for the customer? ex) screening etc?

Q2. Do you have other recommend device for this usage other than SN74AVC4T774?

Datasheet  Rev.E

Datasheet Rev.F

Thanks

Best regards,

Shidara

  • As far as I know, the device itself has never changed. I guess when the 1.1 V measurements were done, all other measurements were also re-done, and resulted in different values.

    Anyway, the propagation delay can only give an upper bound on the maximum speed, because it is possible for the input to receive the next bit even before the output has finished switching for the previous bit.

    The datasheet says 380 Mbps (= 190 MHz), so this will work.

    You should replace all AVC translators with AXC devices, which are faster. (Although the datasheet values are even larger.)

  • In reply to Clemens Ladisch:

    Hi Clemens,

    Thanks for  your advice.

    Let me add the explanation of issue that the customer faces intra-pair and inter-pair skew

    among channels. 190MHz frequency itself is no problem for a channel.

    Would you advise the recommendation in point of skew variation among channels?

    And Why AXC series has larger value in datasheet?

    Thanks

    Best regards,

    Shidara 

  • In reply to K.Shidara:

    Shidara,

    I believe Clemens is referring to more of a functional speed than just the propagation delay. Prop delay is higher in the AXC because of the delay due to the suppression feature. As Clemens mentioned, the device can receive the next bit even before the output has finished switching the previous bit, giving the upper limits of max speed. The max frequency will likely be limited by the output driver so I think 'faster' is referring to the faster transition times since AXC has slightly stronger driven outputs.
    With regards to skew, the skew will be less than 1ns, typically in the hundred of ps range.
    Here's an FAQ on this topic


    Thanks,
    Rami
     

  • In reply to Rami Mooti1:

    Hi Rami,

    Thanks for your advice.

    1, Let me double check that link posted above seems to conclude SN74AXC8T245 can meet skew spec of 500ps.

        Is SN74AXC4T774 as same as SN74AXC8T245 in point of channel to channel skew?

    2, If the load is FPGA case and not so capacitive one, do you recommend AVC instead of AXC because the narrower Tpd spec?

    Thanks

    Best regards,

    Shidara

  • In reply to K.Shidara:

    Hey Shidara,

    Yes, the skew spec should typically meet the 500ps channel to channel skew at a given temperature across different channels from the same device. Note here that this is just what can typically be expected but we don't guarantee it, though.
    For the second question that may more depend on customer preference but in most cases if both Tpd specs fit within the system specs, the AXC should replace any AVC translation devices.

    Thanks,
    Rami