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Original question:

SN74AVC4T245: hot-swappable?

SN74AVC4T245: Any hot-swappable buffer

Kazuhiko Hirano
Genius 13008 points
Part Number: SN74AVC4T245
Other Parts Discussed in Thread: SN74CBTLV16800, SN74CBT6845C, SN74CBT16811C, SN74CBT16800C, SN74CB3Q6800, TCA9511A, SN74CB3Q16811

Hello,

I understood SN74AVC4T245is not a hot-swappable buffer.
My customer is looking for a hot-swappable buffer.
Dose TI have any recommended buffers?

Best regards,

K.Hirano

  • 0
    Guru 276420 points

    What isolation level do you need?

    I do not know of any buffers with precharge. This has to be implemented manually by connecting the I/Os through a 100 kΩ resistor each to a bias voltage. You have to add switches with a precharged signal path.

  • 0 in reply to Clemens Ladisch
    TI__Genius 13008 points

    Clemens,

    My customer would like Level-3, if possible.
    Any app note for  implementing manually by connecting the I/Os through a 100 kΩ resistor each to a bias voltage?
    Or could you explain ho to do that more detailed, please?

    Best regards,

    K.Hirano

  • 0 in reply to Kazuhiko Hirano
    Guru 276420 points

    There is no app note.

    Precharging applies a voltage to all bus lines at the connector of the board being inserted (while the device is not yet active). This voltage is the input threshold voltage (usually VCC/2) of the devices on the bus. This ensures that the disturbances caused by the inserted device do not make any active signal cross the threshold, in either direction.

    I²C switches like the TCA9511A use 100 kΩ; analog SN74CBxxx switches use 10 kΩ. (The resistor value apparently does not matter much.) You can use any of the switches that have precharge (SN74CB3Q16811, SN74CB3Q6800, SN74CBT16800C, SN74CBT16811C, SN74CBT6845C, or SN74CBTLV16800).

    Using discrete transistors is probably not a good idea because you want to disconnect them when the device is active, so you would still need switches.