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INA200 - ORing CMP output

Kawai
Guru 19785 points

Hello Team,

There is a typical schematic in the datasheet page 16, Figure 30. When ORing the two CMP output, could we remove these diodes ?  We believe CMP output is opne-drain, so it seems the oring diodes can be removed. Would there be any adverse effect ?

Best Regards,
Kawai

  • 0
    Guru 19785 points
    Hello Team,

    Could anybody help us on my post ?

    What we would like to know is that if you could remove the diodes when ORing with other open drain devices.

    Best Regards,
    Kawai
  • 0 in reply to Kawai
    TI__Genius 15770 points
    Hi Takushi,

    This question was posted on the wrong forum, I just received it in the CSM forum. I will review your questions and get back to you.
  • 0
    TI__Genius 15770 points
    HI Kawai,

    I reviewed the sample circuit. As I understand the circuit, removing the diodes will depend on your circuit functionality preference.

    A) If you remove the diodes the circuit will work as an OR function. (If any of the CMPout trip, the output will trip). Also the current through the pullup resistors will double.

    B) With the diodes, the circuit will work as an AND function. Both CMPout need to trip so the output trip as well.

    Hope this helps!

    Regards
  • 0 in reply to Mayrim Verdejo
    Guru 19785 points

    Hello Mayrim-san,

    I believe both with or without the diodes, it would work as OR function. Figure 30 is bidirectional over current monitoring schematic which means AND condition can be never met, current could only be flowing in the either way. I was wondering why this application example inserted the diodes.

    So, for the OR application, can we remove the diodes ? We believe there is no problem. Below is what we would like to do.

    Best Regards,

    Kawai

  • 0 in reply to Kawai
    TI__Genius 15770 points

    Hi Kawai,

    The application shown in the Figure 30 is a window comparator with both High current detection and Low current detection. Now this circuit works because we have diodes. In the Open-Drain output config, Pull down is more powerful than Pull up unless some one uses very low resistor which will  burn a lot of power. So connecting them together without Diode will result in following:

    Case 1 - Let you have high Current detection comparator tripped (Pull up is pulling that node high), but we have the low detection comparator driving to zero by open-drain               driver. The Low driver is stronger, so Low one will win. The Output of the combine will be Low instead of showing a high trip (Real Trip).

    Case 2 - When Low is tripped and high is not tripped", same problem will happen.

    The circuit will not work unless you have diode which Blocks the Strong pull down driver when it is driving.

    The Open drain drivers active state is usually Active low, that is why i said they are "ANDED" but as I double check in the datasheet after your comment I see it is active high. So the function is OR. (active state of open-drain being high is a problem, that is the reason we needed diode to connect them)

    We need to confirm if their General device Opendrain is active low or active high.

    If it is active low, they they can't connect like the one they showed in the picture as our device will pull the CMPout low all the time disabling the General device function.

    If it is active high, they can connect but has to connect using diode.

  • 0 in reply to Mayrim Verdejo
    Guru 19785 points
    Hello Mayrim-san,

    Thank you for the detail explanation. I clearly understood that it needs the diodes. Sorry that I was thinking as the open drain output were logic Active Low.

    Best Regards,
    Kawai