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LSF0108: I wonder if LSF0108 is suitable for my TMS320F28X based system.

Sang-il Nam
Expert 2550 points
Part Number: LSF0108
Other Parts Discussed in Thread: SN74LVC4245A, , TXB0108, SN74LVC2G17

Until now, I have used the SN74LVC4245A for the GPIO port of the TMS320F28X chip.
However, I needed a device that was freely available in both directions, so I searched TI's products and found LSF0108.

I plan to use TI's LSF0108 as a bi-directional digital buffer. I'm wondering if there is anything wrong that can be problematic assuming I use LSF0108 for two cases, such as the attached image.

If the LSF0108 is not suitable, please suggest what the appropriate device is.

Thanks in advance.

  • 0
    TI__Guru 62480 points

    Hi Nam,

    In your first case, there is no translation between the 2 devices, what is the purpose of using the LSF0108 device? This device doesnt provide any buffering capability on its own. You may not need the LSF in the 1st scenario.

    In the second case, yes, you can configure the device that way. Also, note that the 5V side would need external pullup resistor to 5V supply to enable up translation. The pulldown resistors on the last 2 lines is indicating that these channels are left unconnected and hence using a pulldown?

    Please refer to the LSF basics and its working in this FAQ:

    e2e.ti.com/.../742100

  • 0 in reply to ShreyasRao
    Expert 2550 points

    Thank you for your quick reply.

    I overlooked that the LSF0108 is not a digital buffer solution.

    Is there a digital buffer solution that can bidirectionally transmit without any direction control?

    It would be better if Schmitt-trigger was applied to the buffer input.

    Thanks in advance.

  • 0 in reply to Sang-il Nam
    TI__Guru 62480 points
    Hi Nam,

    TXB0108 can be considered as a bidirectional buffer solution for the use case you have here.
    however, note that the TXB is weak buffer limited to 20uA drive strength and hence cannot drive large cap loads >70pF.
    By definition, the auto bidirectionality feature of the device makes it a weak driver.
    Please let me know if you have any questions.
  • 0 in reply to ShreyasRao
    Expert 2550 points

    Your advice has been a great help to me.

    I wondered if there was a digital buffer solution that allowed free pull-up or pull-down applying to define the initial state of the signal line, as well as bidirectional signal transmission without direction control.

    And If it was existed, I wanted to apply a digital buffers to my system design that could transmit bi-directional signals without directional control.

    But after hearing your advice, I think it would be better to use a Schmitt-trigger input type digital buffer like SN74LVC2G17.

    Thanks.

  • 0 in reply to Sang-il Nam
    TI__Guru 62480 points
    Hi Nam,

    Glad to help.
    The ST buffer will help if you are looking into any translation.
    but wont be guaranteed for 3.3 to 5V translation and this cannot do bi directional data transmission either.