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INA2332: huge gain difference

first_name last_name21
Prodigy 10 points
Other Parts Discussed in Thread: INA2332

Dear ladies and gentlemen,

I'm using your INA2332 amplifiers in an application with 8 load cells (with 260 Ohm strain gages).
The gain is set to 1000 with Rin=5k1; Rf=1M on all amplifiers, supp. voltage=5V.
To find a problem, I connected a load cell's output  to all amplifiers and I expected to measure the same gains on all amplifiers, but I see that the gain is different by a factor of more than 2.
Also when I vary the (low impedance) voltage which is connected to the REF pin (between 0V and 3V), I see the different gains which amplify the reference. The layout has been made carefully and there is hardly any noise.
What could be the reason for this difference?

Thank you for your help! Best regards, Tobias

  • 0
    TI__Mastermind 25805 points

    Hello Tobias,

    Here are a couple suggestions:

    1)  Try replacing the load cell with a known differential voltage.  Given that your gain is 1000V/V and 550mV<Vcm<3.8V when Vs=5V, a 2mV differential signal with a common-mode voltage of at least 1V should work well (please refer to the figure in the upper right corner of page 5 in the data sheet).  Since the 'gain' changes as you vary the reference voltage, I have a feeling that the input common-mode voltage is <1V.  You will see on the aforementioned figure that for Vcm<1V the output range varies with reference voltage.  Therefore you perceive a change in gain though it's really a limitation of the output swing of the device.

    2)  See if the issue follows the amplifier or the site on the PCB.  In other words, try swapping an INA2332 that is exhibiting inaccurate gain with one that is exhibiting accurate gain.  If the problem still exists, the only variable that was changed is the site on the PCB and re-evaluate your PCB layout.  If the problem goes away, remove the offending INA2332 from the PCB and solder it to a DIP adapter board.  Then try evaluating its functionality on a breadboard.

    I hope this helps!