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INA2126 Gain will not change

Jeff Maloney
Prodigy 10 points
Other Parts Discussed in Thread: INA326

Hello everyone.

I have been trying to get this instrumentation amp to work for a few hours now and I have no clue what I am doing wrong. I am using a function generator to input a sine wave (~20mVpp, 500Hz) into the amp, and no matter what value I use for RG I get the same gain (something like 300). I have used values that the data sheet claims will give me a gain of 10V/V and seen no difference in the output. It is always a clipped waveform coming out. The circuit I'm using is shown below. Does anyone know what I'm doing wrong?

8130.schematic.pdf

Sorry. Here is the schematic.

  • 0
    TI__Mastermind 25775 points

    Hello Jeff,

    Using a single 5V supply and connecting Vref to 2.5V, the linear output swing versus common-mode voltage is shown below:

    Notice that the output cannot swing closer than ~0.8V (typical) to each supply voltage.  Also notice that the common-mode of your input signal should be ~1.5V to ~3.1V for the largest output swing.

    Your schematic shows that the common-mode of your input signal is 0V, which means you're operating outside the linear region of the device.

    You have a few options here.  First, you could try adding a dc offset (say 2V) to your function generator.  However, many generators have limitations on the amount of dc offset you can add.  Secondly, you could operate the device using dual supplies (e.g. +/-2.5V).  This is probably not the desired solution, but it will allow you to get the operation of the device working to further your understanding.  Finally, you could try using a different device that has greater output swing for common-mode voltages closer to ground.  One such example is the INA326.

    One more important thing to note is that you are driving the output of the device with 2.5V.  I assume this is a mistake in your schematic.  I would only drive the reference pin with 2.5V.