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Original question:

TXB0108: TXB0108

TXB0108: Series Resistance Implementation

David Wang60
Intellectual 980 points
Part Number: TXB0108
Other Parts Discussed in Thread: TXB0304, TXB0302

I am planning on using the TXB0108 for a high speed QSPI interface. Is there any issues with using series resistor (<49.9ohms) on the input/outputs since there is a 4kohm already present? I am planning on using series resistance to help reduce any overshoot/reflections or any other SI issues.

Thanks

-David

  • +1
    TI__Mastermind 45795 points

    Hey David,

    No there is no issue with this, but it will effectively limit the speed. I typically see 100 MHz+ QSPI which is already outside of what this device can do. A faster version would be the TXB0304 (4 channel), but you would have to use two to support the 6 channels needed (or use the TXB0302 which is 2 channel).

  • 0 in reply to Dylan Hubbard
    Intellectual 980 points

    We are planning on running the QSPI around 25MHz or so. 

    Also, I saw a few other forum posts about having two TXB0108 in series? The QSPI interface will traverse from one card to another card. We have the TXB0108 being used as a buffer on both sides (no voltage level shifting). From what the other posts are indicating that the output drivers are too weak to drive the inputs. Is there a recommendation of another part to use for this situation or an implementation to be able to use this configuration?

  • +1 in reply to David Wang60
    Guru 316760 points

    Bidirectional signals cannot be buffered (unless you also have a direction signal).

    There is no good solution for QSPI over a long cable. You would have to choose an entirely different protocol.