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INA141

Jackson Lui
Prodigy 20 points

Other Parts Discussed in Thread: INA141

Hi

If INA141 isn't being used, leaving the V+ and V- pins floating might be problematic and at the worst case it can oscillate.

Typically we've been grounding the pins through a 10K resistor when not used.

I wanted to know if I can simply short the pins together (V+ to V-) via a 50mOhm resistor as that is the most convenient for us.

If I do this will there be any chance that I can oscillate or rail to one end?

Thanks

J

  • 0
    TI__Mastermind 25865 points
    Hello Jackson,

    If the INA141 is not being used I recommend not populating the device.

    If it must be populated I would simply leave the supply pins floating. Without supply voltages I don't see how the output can have any voltage, much less oscillate. This assumes that there is no input signal such that the device turns itself on by forward-biasing the internal ESD structures. Though I don't know much about your application or circuit, I find this pretty unlikely.
  • 0
    Prodigy 20 points
    More detail:
    The INA141 will be used to measure a voltage across a sense resistor from two different spots on the board and this will be facilitated via a SPDT relay. When the INA141 isn't being used the inputs to the inamp will be switched away and typically parked by switching in pull downs to avoid oscillation at the output due to floating inputs. I'd like to know if I shorted the input pins of the inamp, would that be sufficient to prevent any oscillation at the output? I think the answer is yes but I'm looking for an official confirmation from TI. thanks
  • 0 in reply to Jackson Lui
    TI__Mastermind 25865 points
    Hello Jackson,

    Thanks for the additional information. In the first post I interpreted "V+" and "V-" as the supply pins, not the input pins.

    Shorting the input pins together without any (or very little) impedance will results in a differential voltage of ~0V. Therefore the output should simply be the reference voltage. Note that depending on your supply voltages, shorting the inputs to ground may be out of the linear operating region of the device. Therefore you may have to short the inputs to mid-supply (e.g. 5V if using a 10V single supply). For more information on the linear operating region of instrumentation amplifiers, please read the following FAQ:

    e2e.ti.com/.../3373.understanding-instrumentation-amplifier-vcm-vs-vout-plots

    If you place a larger impedance between the inputs a differential voltage will be generated based on the input offset current. This differential voltage will then be amplified by the gain, summed with the reference voltage, and that result will appear at the output.

    I cannot say for certain that you will have no oscillations at the output of your circuit because we don't know much about the circuit or PCB layout. In general, though, if you are experiencing oscillations at the output I would first check the load capacitance since this is a common cause of instability. Same holds true for capacitance on the input pins and gain-setting pins. One other concern that I have is the inductance that may be associated with the relay. If you're observing oscillations at the output and you determine it's not due to load or input stray capacitance, try removing the relays and shorting the inputs to mid-supply.

    We have a series of lectures concerning op amp stability that can be found at www.ti.com/precisionlabs. Though the INA141 is an instrumentation amplifier it can still become unstable when driving too much load capacitance. The INA141 data sheet lists 0.001uF as the typical stable load capacitance value.

    Hope this helps!