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AMC1200 Gain Error for Monitoring voltage

Prodigy 40 points

Replies: 3

Views: 662

Hello,

On page 14 of the AMC1200 datasheet there is a diagram showing a voltage monitoring application.

I have a couple of questions regarding this:

1. What is the tolerance of the Rin resistor which is listed as 28kohm in the datasheet.

2. If I include the Rin resitance as part of my calculation for the voltage divider do I still get the extra gain error described by Equasion 1?

3. I am trying to monitor a voltage which is 280Vp, what is the best way to use the AMC1200 to keep the gain error as low as possible.

Thanks;

Leo

 

3 Replies

  • Hello Leo,

    1) We do not have a distribution for the change in input differential resistance of the AMC1200. If this input resistance plays a significant role in your design my recommendation would be to assume Rin could fluctuate between 24 kohm and 39 kohm from unit to unit.

    2) Yes, that is correct.

    3) The best way to keep the gain error as low as possible is by choosing R2 as low as possible.

    Best regards,

    Jose

  • In reply to Jose Duenas:

    So in order for me to keep the gain error below say 0.7% I would need to pick R2 such that R2/24k <=.002, that would mean that my R2 resistor needs to be 48ohm and this is just not feasible for our application...

    Does TI have any other isolation amplifier offerings that would allow for a much larger resistor say in the 1kohm range and still give me a gain error of <1% over all?
  • In reply to Leonid.Y.Ayzenshtat:

    Hello Leo,

    We do not have other isolation amplifiers with higher input impedances.

    However, you can include an amplifier in front of the AMC1200; depending on your input offset requirements have a couple of options:

    a)      You could use a simple op-amp used in a similar way to that used in TIPD129:
    http://www.ti.com/tool/TIPD129
    http://www.ti.com/lit/ug/tidu040a/tidu040a.pdf
    //

    b)      You could use an instrumentation amplifier like the INA333 in conjunction with the LM7705.

    Best regards,

    Jose

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