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TXS0108E: TXS0108E

Shams Syed
Prodigy 40 points
Part Number: TXS0108E
Other Parts Discussed in Thread: TXU0102, TXS0102

TXS01018 having a problem driving 68 ohms terminated line to CMOS logic low at the B outs. We are currently using TXS0108E to translate CMOS 3.0 V logic to CMOS 3.3 V logic and also to drive 68 Ohms terminated lines. See our application diagram below: 

Any help is appreciated

  • 0
    TI__Mastermind 33755 points

    Hi Shams,

    Please note that the schematic isn't complete. However, note that TXS is also a passive switch, so it does not reduce the low voltage of any signals. With the TXS also having internal pull-up resistors, you should not be needing external ones. 

    The issue is most likely causing the edge accelerators to trigger and would further recommend shorter traces and without connectors or cables.

    I would also recommend just connecting the OE directly to VCC to keep the device always enabled (as long as you don't care about the state of the I/O during power up).

    Note that the TXS0108 has dynamic internal pull-up resistors as rising and falling edge one-shots and would further recommend using TXS0104 for the 4 channel signals/application (TXS0102 for 2 CH) if bi/auto directional signals are used. If the signals are in fact Uni directional, I recommend using TXU0102, thanks.

    Best Regards,

    Michael.

  • 0 in reply to Michael Ikwuyum
    Prodigy 40 points

    TXS0108E has internal one shot circuit. Does it have a latch type one shot to latch high or low? 

    Can TXS0108E drive 75 ohms load terminated transmission lines? Also, do you have any data showing the TXS0108Edriver ac source impedance?

  • 0 in reply to Shams Syed
    Prodigy 40 points

    Also, I have a question regarding internal Npass circuit; What is the value of R1 and R2 shown and how does it work? 

  • 0 in reply to Shams Syed
    Guru 282540 points

    The one-shot does not latch; it is intended only to speed up signal edges, and is active for a few nanoseconds.

    The TXS is a passive switch and does not have any drive strength.The internal pull-up resistors are not strong enough for such termination.

    R1 and R2 model the on-resistance on the switch; it's 1000 Ω in the worst case.

  • 0 in reply to Clemens Ladisch
    Prodigy 40 points

    Your TXS0108E spec has +/- 50 ma source and sink drive current: 

  • 0 in reply to Shams Syed
    TI__Mastermind 33755 points

    Hi Shams,

    The above is for the maximum max ratings that can break and cause damage to the device and not the recommended for normal operating conditions.

    Please refer to section 6.5 of the datasheet for the  ICCx. thanks. 

    Best Regards,

    Michael.