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TLV1702-Q1: Window Comparator Output is High When GND Disconnected

Reddy
Prodigy 150 points
Part Number: TLV1702-Q1
Other Parts Discussed in Thread: TLV1702

The Above Circuit is Designed to satisfy below requirement:

1. HIGH FOUT When LED Is Normal

2. LOW FOUT When LED is Fail Open

3. LOW FOUT When LED is Fail Short

4. LOW FOUT When VCC is Disconnected

5. LOW FOUT When GND is Disconnected.

High Signal Corresponds to 10V or Higher, Low Signal Corresponds to less than 5V

The above Circuit is able to satisfy all the 1-4 Requirements.However, when the Ground is disconnected, it is reading High 12V Signal.

What Changes are required to make it LOW when GND is disconnected.

  • 0
    TI__Mastermind 26510 points

    Reddy

    I presume you are saying that the GND for the LED is disconnected and not the GND for the TLV1702.  If that is the case, then GND disconnected to the LED would be equivalent to LED is an open and the output of the comparator would be LOW.  However, if you are also disconnecting the GND of the TLV1702, the output will be high because the comparator requires GND to function.

    Chuck

  • 0 in reply to Chuck Sins
    Prodigy 150 points

    The Circuit is already on PCB, it goes inside a Panel Mount Indicator Light, 12V.

    Disconnection of Black wire disconnects the ground from both LED and Opamp.

    In such condition, the requirement is to get no signal out.

    Because it's an open collector Output, I was reading 12V when Ground was disconnected.

    Can you suggest a modification to fix this?

    How about using a PushPull type Comparator ? or Using a PNP transistor towards Input or Output? to make output low when GND is disconnected?

  • 0 in reply to Reddy
    TI__Mastermind 26510 points

    Reddy

    Sorry for the delay but we were off on US holiday break yesterday.

    I would connect a p-channel MOSFET between FOUT and whatever FOUT is connected to.  The source of the MOSFET would be connected to the output of the comparator.  The gate would be connected to the GND connection point, and the drain would be the wire that comes off of the board and becomes the new FOUT node.  I would also add a resistor between the source and gate to make sure that the p-ch MOSFET remains off when the GND is not connected.  Under normal operation when GND is present, the p-channel MOSFET will act like a low impedance switch.  However, when the GND is disconnected, the MOSFET will look like an open switch.

    Hope this helps solve your problem of having no output when GND wire is disconnected.

    Chuck