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Using the ADXRS620 with a Vratio voltage lower than AVcc

Thread Summary

The user inquired about using the ADXRS620 with a 2.5V ADC reference. The support engineer advised that while the ADXRS620 can operate with a 2.5V Vratio, it is not characterized below 3V, potentially increasing ratiometricity error. The Vratio pin draws about 85uA at 2.5V, which is steady and unlikely to cause noise issues for other ADC channels.
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Hi,

    I want to use the ADXRS620 with an ADC with an Full Scale output voltage of 2.5v.

As far as I can see, there are two ways I can do this.

  1. Put a voltage divider on the RATE_OUT to divide the FS down to 2.5 before connecting to the ADC.
  2. Drive Vratio from a 2.5v reference source and connect RATE_OUT directly to the ADC input.

As I already have a 2.5v reference in my application, option 2 seems the better choice as it save 2 resistors. However, the datasheet doesn't give me enough information to be sure this is the best choice.

Can you answer the following questions for me please?

  1. Will the ADXRS620 operate correctly if Vratio is 2.5V?
  2. How is the accuracy of the part changed if I use a 2.5v Vratio?
  3. How much current does the Vratio pin draw at 2.5v?
  4. Is this a steady state current or could connecting the Vratio pin to my clean 2.5v reference cause noise issues for other ADC channels which share this reference?

Thanks

  • Hi,

    The ADXRS620 has not been characterized at Vratio below 3V.  It should work with a 2.5V reference, however you might increase ratiometricity error.  In other words, the null output may not be at 1.25V and the positive and negative swing may be lower.  It would be best to use a reference of 3V or higher.

    The Vratio pin has a loading of ~30KOhms, so it will draw ~85uA at 2.5V.  It's steady current and will not cause any noise issues.

    Regards,

    Venkat

  • Hi Venkat,

                   thanks for clearing that up for me. I couldn't find any reference to a min limit on the datasheet.

    Rgds,

             Bill

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