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TXU0104: TXU0104 maximum frequency

Vincent Marsaud
Prodigy 80 points

Part Number: TXU0104
Other Parts Discussed in Thread: LSF0204

Good Morning.

I'm using TXU0104 component to translate signals from +1,8V to +3,3V and the inverse, from +3,3V to +1,8V.

In the datasheet, I have seen that 50Mbps minimum data rate is indicated, but not the maximum. As the maximum propagation delay is 8ns, I made the guess that the maximum data rate should be 125Mbps (1/8ns).

Considering an input signal with a duty cycle of 50%, do you confirm that injecting an input signal with a frequency of 50MHz will work ? 

Thanks per advance,

Vincent 

  • +1
    TI__Mastermind 38610 points

    Hello Vincent,

    For the data rate spec table, min actually means max for us. Apologies for the confusion.

    Since 50Mbps translates to 25MHz, then providing an input signal of 50MHz won't work.

    Regards,

    Josh

  • 0 in reply to Joshua Salinas
    Prodigy 80 points

    Hello Joshua.

    Thanks for your answer.

    So you also mean the 8ns delay from the datasheet is minimum instead of maximum ?

    Sincerely,

    Vincent

  • 0 in reply to Vincent Marsaud
    TI__Mastermind 38610 points

    Hello Vincent,

    No, this only applies to the maximum rate table.

    However, I don't see the 8ns max delay you are referring to

    Regards,

    Josh

  • 0 in reply to Joshua Salinas
    Prodigy 80 points

    Hello Joshua.

    Thanks for your answer.

    You're right, I was not looking at the correct parameter (output skew), not the propagation delay...

    Please, can you also explain the following test condition : what means "50% Duty Cycle Input" when indicating a data rate of 50Mbps (cf. down translation 3V - 3.6V -> 1,65V - 1.95V) ? Does it means you're injecting a 25MHz signal on the input ?

    Does TI have a TXU0104 cross reference which allows 100Mbps for Up and Down translation ?

    I have found the LSF0204 TI cross reference. Except the fact it requires external pull-up, I have to check the total capacitance line. But with a value < 30pF, it should work. Do you confirm ?

    Sincerely,

    Vincent

  • 0 in reply to Vincent Marsaud
    TI__Mastermind 38610 points

    Hello Vincent,

    Duty cycle is the percentage of one period in which a signal is on and typically given as a percentage. A 50% duty cycle means the period when the signal is on and off are the same. The frequency does not change.

    For 1.8V <-> 3.3V translation, I would recommend looking into SN74AVC4T. If you are needing a level translator for SPI, I would recommend SN74AVC4T774. This part allows you to configure each I/O independently. 

    If you only need the signal to flow in one direction, I would recommend SN74AVC4T245.

    Regards,

    Josh

  • 0 in reply to Joshua Salinas
    Prodigy 80 points

    Good Morning Joshua.

    I made a measure of injecting a square signal with a frequency of 40MHz at the input, with VCCA = 3,3V and VCCB = 1,8V.

    The output signal looks like a sinus format but I obtains the correct frequency at the output.

    Why are you saying it shouldn't work ? Is it because the output signal doesn't have a square format ?

    Do you have information on the TXU0104 internal circuitry stage ? Is it composed of gates ?  does it include filtering ? If yes, what is the short cur frequency ?

    Sincerely,

    Vincent

  • 0 in reply to Vincent Marsaud
    TI__Mastermind 38610 points

    Hello Vincent,

    By sinus, do you mean "sine" wave? The issue is not with up translation (1.8V -> 3.3V) but with down translation (3.3V -> 1.8V) since it only supports up to 50Mbps or 25MHz.

    Now that being said, we set conditions on what we consider a passing signal, see table below. If your application is able to take 40MHz sine wave from TXU0104 then no device change is needed.  

    Regards,

    Josh