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INA207 - comparator output - normally high when off

Daniel Beaudoin
Prodigy 40 points
Other Parts Discussed in Thread: INA207

I am using the INA207 as a replacement of the MAX4375.  Its larger input voltage range is an advantage and we started using the INA207 as a product replacement and for new designs.  The exact part number I am using is INA207AIDGS.

If I apply 3.3V though a pull-up resistor to the CMP2 OUT pin with the remaining of the circuit unpowered, the open drain output is in an undefined state.  In my circuit, the reset pin is connected to the ground

With a 10k resistor, the output is around 1.5V

With a 1k resistor, the output is around 2.0V

With a 100 ohm resistor, the output is around 2.2V

This unfortunate semi conductive open drain behavior is considered as an overcurrent detection in my circuit and the system cannot turns on.

I would like to know if there is a way to use the INA207 with a defined comparator output state at startup ?

 

 

 

 

  • 0
    TI__Expert 4115 points

    Daniel,

    With the information that you have provided it appears that you are utilizing more than a single supply.  One supply to provide 3.3 V for the pull-ups and another to supply the IC.  Is this correct?  I am just trying to verify that the IC has no power while you are taking the measurements you have specified.

    Also, can you provide any information on the impedance of your load?  With no power to the IC you should see a voltage division on the output due to the pull-up resistor and the load with 3.3 V as the input voltage.

    Thank you.

  • 0 in reply to Jared Casey
    Prodigy 40 points

    You are right, I am using 2 different supplies but they all have the same ground.

    While I take the measurement, the whole circuit is off and I apply only a 3.3V through an external pull-up on that pin. Then I measure the voltage on the pin.

    On the output of the comparator, there is no load.  The output is directly routed to a connector. The normal pull-up is external to that board.

     

    Thank you

     

    Daniel

     

     

  • 0 in reply to Daniel Beaudoin
    TI__Expert 4115 points

    Daniel,

    I build a quick test circuit with the INA207 and I was not able to reproduce the issue.  The INA207 DS does not specific the behavior of the device when not powered, so this would be considered an undefined state.  Can you change up the squencing of your system so as to give the INA207 power earlier?  Have you tested the device when power is applied?  If so, do you see expected results?  I know that you mentioned your system will not start up, but I am curious to see how the device operates when power has been applied.   Have you tried swapping out the current device and using another device? In other words, do you see the same issue across multiple INA207s?  Also, would you mind providing your schematic? 

    Thank you.

  • 0 in reply to Jared Casey
    Prodigy 40 points

    How have you done your quick test ?  What pin have you connected to GND ?  This is the circuit.  At startup, VCC_3V3 and -VCC-12VA and -VCC_12VA_S are all at 0V.

    I cannot power earlier the INA207.  I have not tested the circuit with power applied.  But, when I remove that device, the system starts up correctly and works.  I have the same issue with all the board tested.

  • 0 in reply to Daniel Beaudoin
    TI__Expert 4115 points

    Daniel,

    I have been able to reproduce the issue that you have with your test circuit.  When the device does not have power it appears that some undefined current paths are created, possibly ESD cell leakage, when the device is not powered but power is at the output of the comparator (via the pull up resistor).  If you can find a way to apply power to the device you will see expected behavior.  We do not characterize the IC in a powerless state.  So, we cannot provide information on the device behavior in this state.

    I have a limited scope on your application, so it will be difficult to provide meaningful suggestions.  Could you possibly combine the two 3.3 V rails that you have so that power will be applied to the device the same time power is applied to the output?

  • 0 in reply to Jared Casey
    Prodigy 40 points

    Thank you for the answer.

    You have confirmed the behavior of the open drain output when the device is unpowered.

    For this design, I cannot really change the circuit, so I will need to remove the functionnality of that device.

    Best regards

    Daniel