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SN74AXC4T774-Q1: Driving strength question

Oliver Lin
Expert 3825 points
Part Number: SN74AXC4T774-Q1
Other Parts Discussed in Thread: SN74AXC4T774, TXB0104, TS3DS10224, TXU0304-Q1

Tool/software:

Hi team,

Customer is using SN74AXC4T774 - Q1 for SPI interface. Is there any limitation of the layout?

Please see below for 2 paths, the data rate is at least 16.67MHz, Max 33MHz. Below waveform is showing that voltage drop during the transition. Is that ok to use TXB0104 to sovle this problem?

  • CPU->Level shifter->TS3DS10224->ROM
  • CPU->Level shifter->TS3DS10224->PFR Module->ROM

  • 0
    Prodigy 30 points

    The narrative is partially incorrect.

    We use PI4ULS3V504AZMAEX now, but there's a problem of the waveform.

    So we want to change to SN74AXC4T774 - Q1 or TS3DS10224(pin to pin).

    Thanks

  • 0
    Guru 290440 points

    The TXB is not a buffer; do not use it.

    A possible replacement would be the TXU0304-Q1, but it has slightly lower drive strength.

    You have ringing at the signal edges. To avoid this, properly terminate the signal lines; the most common way is to reduce the driver's drive strength with source termination.

  • 0 in reply to Hungyi Hsu
    Prodigy 30 points

    Fixed description, is change to SN74AXC4T774 - Q1 or TXB0104.

  • 0 in reply to Clemens Ladisch
    Prodigy 30 points

    Hi Celmens

    Because we are currently using PI4ULS3V504AZMAEX.

    And it is recommended that the trace length shorter than 4 inches.

    Otherwise, when the delay time of the trace is longer than the one-shot time, there may be an unexpected status.

    Does TXU304-Q1 has the recommended limit of trace length?

    Because of the placement limit,trace length on PCB is very difficult to reduce.

    Thanks

  • 0 in reply to Hungyi Hsu
    Guru 290440 points

    The PI4ULS3V504AZMAEX and the TXB0104 are pretty much identical.

    Buffered level shifters like the SN74AXC or TXU work in one direction per channel, so they do not need one-shots, are much more robust, and work with much longer traces.

    Drive strength at 1.8 V: TXB: 20 µA; TXU: 4.5 mA; SN74AXC: 8 mA.