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ADS1263: Using OP Amp to drive ADS1263

Intellectual 1155 points

Replies: 1

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Part Number: ADS1263

Hello,

I am using the ADS1263 and had a question.  If using an op amp to drive it, same power supplies, is it a good idea to place a resistor between op amp output and ADC input.  We do have filtering about the op amp.  I am more wondering, if the op amp goes to rail, although as stated all parts on the same supply, is there some overdrive possible with internal ESD diodes.

 Thanks,

Adam

  • Hi Adam,

    The ESD diodes on the ADS1263 analog inputs will turn on at voltages lower than AVSS-0.3V and voltages higher than AVDD+0.3V. If the op-amps are powered by the same 5V "AVDD/AVSS" supply, then I don't think there is any concern that you'll exceed either of these limits.

    Nevertheless, you could always add a small RC filter to the output of the op-amp to assist with noise filtering. In this case using larger resistor values will provide you with a lower cutoff frequency and more current limiting during an electrical over-stress (EOS) event. Input current should never exceed +/- 10 mA, per the "Absolute Maximum Ratings" of the ADS1263. However, I would not recommend making this resistor much larger than a few kOhms, as the thermal noise of the resistor will start to degrade the noise performance of the ADC.

    As an aside, I would recommend reconsidering if the use of an external opamp prior to the ADS1263 is truly necessary... The ADS1263 provides a very low noise PGA with a broadband noise density of about 7nVrms/sqrt(Hz) and virtually no 1/f noise. Most discrete opamps will not be able to achieve this level of noise performance, and will tend to degrade the system's overall resolution, when compared to using the ADS1263 by itself. Unless you need an active filter or need to allow for a wider input voltage range, generally the internal PGA of the ADS1263 will perform better, even with its maximum gain of 32 V/V.

    Best regards,
    Chris Hall
    Applications Engineer | Precision ADCs


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    TI Precision Data Converters | TI Precision Labs - ADCs | Analog Engineer's Calculator | Data Converters Learning Center | Selection Guide

     

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