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LSF0108: Please let me know whether external pullup resistors are needed on PortA and PortB when unidirectional signals are outputted from them.

Shinsuke Tanaka
Intellectual 520 points
Part Number: LSF0108

Dear Sirs or Madams,

I know understand as follows;

  -When unidirectional signals are outputted from PortA pins, we do NOT have to add external pullup resistors on PortA pins because

   the voltage on these pins are driven to VrefA pin's voltage by this IC.

  -When unidirectional signals are outputted from PortB pins, we have to add external pullup resistors on PortB pins because

    the voltage on these pins can NOT be driven by this IC. The voltage should be driven by external pullup resistors.

Are above my understandings correct?

Best regards,

Shinsuke Tanaka

  • 0
    TI__Guru* 97046 points
    Hello Tanaka-san,
    I would highly recommend watching the videos I linked in the other LSF0108 thread you posted. If you still find anything confusing, please return and let me know what needs clarification.
  • 0 in reply to Emrys Maier
    Intellectual 520 points
    Dear Emrys san,
    I appreciate your rapid response.
    I now know that my previous understandings are incorrect and I understand that the followings are correct;

    -When unidirectional signals are outputted from PortA pins, basically we have to add external pullup resistors on PortA pins.
    But, only when the total leakage current of receiver pins connected to each PortA pin is less than 1uA, we can remove external
    pullup resistors from PortA pins.
    -When unidirectional signals are outputted from PortB pins, we have to add external pullup resistors on PortB pins because
    the voltage on these pins can NOT be driven by this IC. The voltage should be driven by external pullup resistors.

    My question is resolved and I don't have further questions.

    Best regards,
    Shinsuke Tanaka