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Open collector/drain troubles

  1. Aug 22, 2010 #1
    Hi everyone.

    I have a digital circuit which is supposed to talk to a temperature detector. The detector speaks open drain I2C (and it is a slave of course).

    My problem is not with I2C but is instead the following. The data line for the detector is, on the other side, the driver input and receiver output of a differential / single ended transceiver, the DS92LV010A (www.national.com/ds/DS/DS92LV010A.pdf[/URL]). By the way, I didn't build this PCB, I'm just trying to use it.

    When the transceiver is set for driver input (input from the detector), I have found that it pulls the voltage of the SDA line down to 0 more strongly than the required pullup resister can counteract.

    Is it impossible to use this transciever for open drain?
    Please let me know if more information would make my question more answerable.

    Thanks
     
    Last edited by a moderator: Apr 25, 2017
  2. jcsd
  3. Aug 22, 2010 #2
    A schematic would help... I'm also confused about the directions of things. You say:
    "When the transceiver is set for driver input (input from the detector)...it pulls the voltage of the SDA line down..." If it's an input it shouldn't be pulling anything down, or is the SDA line on the output of the transceiver that is trying to do input? If so, it should eventually also pull up, no? And I'm not clear where the open-collector thing comes into play.

    Schematic schematic schematic....
     
  4. Aug 23, 2010 #3

    berkeman

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    Staff: Mentor

     
    Last edited by a moderator: Apr 25, 2017
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