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LSF0102: About LSF0102 output ability

Vera Mao
Expert 5065 points
Part Number: LSF0102
Other Parts Discussed in Thread: SN74LVC2T45, SN74AVC2T45

hi dear supporting team,

as for LSF0102, if operate it in push pull mode, how about the drive ability of the output port? 

customer request 20mA output ability,  i.e. they hope this chip could operate like a buffer.  could they?

in the d/s, there is one spec Ipass of 64mA, is this the spec for only show the current capacity? (output current equals to input current) .  tks!

  • 0
    Guru 316640 points
    The LSF devices are passive switches; they have no drive ability whatsoever.

    How much load you can put on the output is determined by the drive strength of the device that actually drives the LSF's input, minus the LSF's on-resistance.
  • 0 in reply to Clemens Ladisch
    TI__Expert 5065 points

    hi Clemens,

    thank you for the reply!

    one more question:  if customer use it for push pull application, should they connect a pull up resistor?  if not, what's the consequence of putting an Rpu ? (customer want to share the circuit for OD and push-pull) tks!

  • 0 in reply to Vera Mao
    Guru 316640 points
    The LSF is not a push-pull device; it never drives its outputs actively high. If an input is in the high state, it switches off the pass transistor and relies on the external pull-up to get a defined high voltage level at the output.

    Is the 20 mA drive strength required for the low level, or the high level, or both?
  • 0 in reply to Clemens Ladisch
    TI__Expert 5065 points
    hi Clemens,
    thank you for the answer!
    yes, they need 20mA for both.
    so do you mean even if the driver side is push pull kind interface, LSF still need pull up resistors at both input and output? tks!
  • 0 in reply to Vera Mao
    Guru 316640 points
    LSF needs pull-ups at any output. (When you're not actually using it for bidirectional signals, some pins are not outputs.)

    Auto-direction-sensing devices cannot have a high drive strength, because they must allow some other device to override the signal.

    Look at direction-controlled translators. 20 mA is more than the SN74AVC2T45 could handle, so the only choice is the SN74LVC2T45.