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TXB0101: Driving capability problem

Part Number: TXB0101
Other Parts Discussed in Thread: SN74LVC1T45, SN74AXC1T45, TXB0102, SN74LV1T125, SN74LV1T34, SN74LVC1G17, SN74LVC1G34

Dear Team,

Currently, my customer faced a problem of TXB0101. They used TXB0101 to be the switch of DMIC's Clock.

From the clock output waveform below, it seems like TXB0101 doesn't have enough driving capability. 

Do we have another solution or digital buffer that could meet their requirement? 

I would be better if the solution has EN pin.

Clock at input.

Clock at output.

  • Hey Jim,
    Is this a unidirectional clock translation application, or do they need the auto-bidirectional capabilities of the TXB0101?

    I would usually recommend a translating buffer such as SN74LVC1T45 for a clock translation application.

    If they need lower voltages (as it appears they do), I would recommend the SN74AXC1T45.
  • Hello Emrys,

    Thanks for the comments. Sorry about that I should change the title as TXB0102 instead of TXB0101.

    We just found that the datasheet has a description as below in yellow. But we leave the unused pin floating. Please check my schematic below.

    Is it possible the root cause of the bad clock output? 

  • Hey Jim,
    No, I wouldn't expect that to be a problem with TXB. Each channel acts as a weak latch, so even if they are not terminated properly, they would maintain a valid logic state (although that state would be unknown).

    I can't see from the schematic what is connecting to A1 or B1 (pins labelled D2, A2). It's likely that there's a load that is too large for the TXB to drive, which is why I would recommend going with one of the unidirectional translating buffers instead - they are designed to handle this type of application.
  • Hi Emrys,

    Understood. But both SN74LVC1T45 and SN74AXC1T45 don't have enable pin so that we can't control it.
    Do you have another solutions with EN pin? Our requirement is 3MHz clock with 22 ohm  + 62pF loading, and VCCA,VCCB are 1.8V. 

    Thank you.

  • Hi Jim,

    Maybe I did not spot it in the text or schematics, but what is the translation requirements?

    You could consider using the SN74LV1T125 which is a unidirectional translation device with output enable capable of driving cap loads and will work at 3Mhz without issues. The Vcc must be tied to the desired output voltage.

    It can work from 1.8V signal input to 2.5V, 3.3V output but the theshold voltage doesnt allow it to work for 1.8V to 5V translation.

    Let me know if this works for you.

  • Hi Sirs,

    Please allow me to update our question.

    If there is no another suggestion of switch, can I use TXB0102 and connect A1/A2 together as well as B1/B2?

    Does these way enhance the driving? Thanks!!

  • Hi Shu-Cheng,

    connecting the IOs together enhances the driving, but not by much. These auto bidirectional translators are not really meant for buffering and high drive.
    I assume that these signals are unidirectional, I would encourage you to consider using unidirectional buffered devices like the SN74LV1T34/ SN74LV1T125.
    I do see that the Vcca and Vccb are both at 1.8V which means there is no translation requirement. In this case, you could also consider regular buffers such as the SN74LVC1G34 or SN74LVC1G17(Schmitt trigger).
    LVC provides up to 32mA at 5V and 4mA at 1.8V.
  • Hi ShreyasRao,

    Our customer would like to use SN74LV1T126DCKR, how much capacitance in theory can the IC support on output trace?
  • Hi Jim,

    We cannot guarantee the capacitance supported with the device, however, we can guarantee that the device can support 8mA of drive current at 5V level.
    With the 8mA(assuming constant current), it could theoritically support any capacitance with the tradeoff being the propagation delay & rise time of the signals increasing with higher cap loading.