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INA827: Effect of voltage reference chip on amplifier performance

Kiron Sen
Prodigy 60 points
Part Number: INA827
Other Parts Discussed in Thread: REF3425, , OPA330, REF3225, INA821, OPA320

I am considering using the REF3425 voltage reference to bias the output of the INA827 instrumentation amplifier by 2.5V. I have two questions:

  1. The REF3425 voltage reference requires at least 0.1uF of output capacitance. Will this capacitor negatively affect the performance of the instrumentation amplifier for high-precision measurements? If so, how?
  2. Would a resistor divider and buffer (eg. OPA330 as suggested by the datasheet) provide better performance?

Thank you!

  • 0
    Guru 140200 points

    Hi kiron,

    have you read section 7.3.7 of datasheet? There's a REF3225 recommended for this purpose.

    The voltage should be able to soure AND sink current (depends a bit on how you supply the INA827). The decoupling cap at the output of voltage reference is not bad at all. But please don't mount it when using a OPAmp buffer instead of voltage reference chip. Otherwise you will erode the phase margin of OPAmp and end up in instability.

    The voltage reference chip should provide a low output impedance. Otherwise the resistor balance of differential amplifier gets worse and the common mode rejection ratio detoriates.

    The REF3425 provides an output current of +/-10mA. That's good. I would chosse a big output cap as discussed in section 10.2.2.1.

    Unfortunately, I cannot say anything about the output impedance of REF3425. But Marcoo Z from the TI's "power management forum" should be able to help you with this.

    Kai

  • 0
    TI__Genius 10850 points

    Hi Kiron,

    Thank you for your post, I can help you. Take a look at section 7.3.7 of the INA821 datasheet. Here we show a few ways to connect the REF pin. I have attached an image below as well:

  • 0 in reply to Tamara M Alani
    Intellectual 895 points

    Hi 

    Is this explanation applicable to INA821 also?

    I am using the INA821 with a reference voltage of 0.25V which was taken from REF5025 -> a potential divider circuit [ 1k/(1k+9k) ] -> and a buffer designed by OPA320.

    I am using two INA821 in my circuit and both are using this 0.25V

    Please advise whether it requires any cap to the ref pins of INA821 or to the output of OPA320?

    Because 9.1.1 part of the datasheet didn't have much content related to the above post.

    Thanks and regards,