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TLV9061: Vin on noninverting input raising V+ pin when opamp is off.

AJay
Prodigy 30 points
Part Number: TLV9061
Other Parts Discussed in Thread: TLV7031, LM393LV, TL331LV, TL391LV

Hello!

I'm using this exact part: TLV9061SQDBVRQ1. I have built the following circuit, with the addition of a 10K pulldown on SHDN. 

When I apply a voltage Vin at the non-inverting terminal, the same voltage - a few mV shows up on the V+ pin. If I connect a 100k resistor between 5V & GND, 200uA of current flows. Why is there so much current going into the noninverting terminal through to the V+ pin?

In the context of my circuit, low consumption is critical due to a battery powered application. The opamp is being used as a comparator to shutdown a 5V regulator after the battery has dropped below a certain level. Everything works fine, except for the when the circuit turns off, SHDN goes low, 5V circuit is turned off, Vin from my battery is still making it to to 5V rail, which is enough to turn on several transistors and several hundred uA slips through continuously. 

 

  • 0
    Prodigy 30 points

    When 5V is turned off, Vin at 3V is much greater than V+ +0.2V....

    Will rethink the circuit

  • +1
    Guru 271360 points

    Applying a voltage at the inputs while the power supply is off violates the absolute maximum ratings. (A current will flow through the input ESD protection diodes into V+.)

    The purpose of the shutdown function is to allow the opamp to stay connected to the active power supply. If the power is off, then there is no difference between the TLV9061S and TLV9061.

    You should redesign your circuit so that the opamp's supply always stays on. Alternatively, use a comparator with overvoltage-tolerants inputs, e.g., LM393LV/TL391LV/TL331LV or TLV7031.