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TIDA-01063: Instrumentation Amplifier with single supply

Part Number: TIDA-01063
Other Parts Discussed in Thread: INA821

Hi,

I have a design that is based on the TIDA-01063 reference design and am using INA821 instrumentation amplifier. The design works fine with dual supply +-3.3V but when trying to use the amplifier with single supply 5V and 2.5V VREF there is no output. Is it possible to make this design work with a single supply ?

  • Hi Einar,

    I don't believe we've tested with a single supply, but I don't see any obvious issues with using it in that way either.  Can you please describe a bit more about how you adapted the design?  For example, are the ground reference connections shown for the coil (at the front end to the INA) referenced to 2.5 V with the INA's -VS at 0 V, +VS at 5 V, and REF at 2.5 V?  Have you confirmed these values with a voltmeter to make sure the circuit is operating as intended?  And, when there is no output from the INA do you see the output stuck at 0 V, 2.5 V, or 5 V?  What do you observe at the input to the INA (in terms of common mode voltage and differential signal when measuring current)?

    If you can share a schematic showing the front end circuitry that could be helpful as well.

    Regards,
    Max

  • Hi Max,

    This is the schematic. For the single supply test I connected the -3V3 to GND, 3V3 to 5V and VBIAS to 2.5V. The output is stuck at 2.5V. 

  • Hi Einar,

    The INA821 should typically have the input signal be between (V-) + 2 V and (V+) - 2 V.  The GND connection on R4 and R9 will cause the common mode at the input to be biased to 0 V.  I think in the case of a single supply it would be better to center this common-mode bias to V+/2 (2.5 V in this case).  Is that possible in your set-up?

    If that change does not work then it would be good to validate the input signal to the INA stage on an oscilloscope to make sure the issue is not with the coil output.

    Regards,
    Max

  • Hi Max,

    Of course this solved the issue. When the common-mode bias was connected to 2.5V it worked.

    Thank you.