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ADS8598H: PGA280 (*8) as a front end to ADS8598H?

Steve Squires
Intellectual 370 points
Part Number: ADS8598H
Other Parts Discussed in Thread: PGA280, ADS131E08, OPA192

Hi,

I'm considering using an 8 channel ADC such as the ADS8598H (+-10V). I also like the functionality (a good number of gains) offered by the PGA280 along with its robust input protection features. My requirements is for a multi-range input from +-10mV to +-10V.

However, in order to pair the two (yes, I know I will need a PGA280 for each channel), I will have to convert the unipolar output (0V-5V) of the PGA280 back to a bipolar +-5V (10V range) with another op amp.

Is this a good approach or is there a better way to achieve my requirements?

Thanks,

Steve

  • 0
    TI__Mastermind 35540 points

    Hello Steven,

    Thanks for your query on E2E.

    Regarding your example, if your signal to ADC is 0~+5V and ADC's input range is +/-5V, you will lose half dynamic range of your ADC. Can you please let me know if the simultaneous sampling is necessary in your application? thanks.

    Best regards

    Dale 

  • 0 in reply to Dale Li
    TI__Mastermind 35540 points

    Hello Steven,

    ADS131E08 is another good solution with PGA280, please refer to below link for more details:

    www.ti.com/.../ADS131E08

    Please let us know if you have any question. Thanks.

    Best regards

    Dale

  • 0 in reply to Dale Li
    Intellectual 370 points
    Hello Dale, thank you for your replies.

    Simultaneous sampling is critical to my application, as is 18 bit sampling at or above 200ksps (the device you suggest is 64ksps). I have also considered delta-sigma ADCs such as the AD7768 (but this introduces other complexity such as the need to add a driver for each channel and an external reference - I'm also not sure about the latency of that device compared to SAR).

    My plan was to use the +-5V range on the ADS8598H plus a level-shift and doubling (or*3 or *4) of the PGA280 0V to 5V output, thus utilising the whole range of the bipolar ADC.

    Steve
  • 0 in reply to Steve Squires
    TI__Mastermind 35540 points
    Hello Steven,
    Based on your information, ADS8598H is a good and suitable solution for you, this is an integrated device with good performance. Please let us know if you need any further support on this device. Thanks.

    Best regards
    Dale
  • 0 in reply to Dale Li
    Intellectual 370 points

    Hi Dale,

    What type of amplifier would you recommend to go between the PGA280 and the ADS8598H to convert from unipolar to bipolar? Do I need anything special to drive the SAR? What if I want to drive a delta-sigma ADC?

    I think a gain of 3, along with a level shift, will give me 13.3V to 9.5mV fullscales.

    Thanks,

    Steve

  • 0 in reply to Steve Squires
    TI__Mastermind 35540 points

    Hi Steven,

    ADS8598H has integrated ADC driver along with LPF filter and PGA (please refer to Figure 52 in datasheet), so the front-end circuit design will not be critical to drive ADS8598H like other switched-capacitor input structure SAR ADC. A low noise, low offset and drift amplifier can be used, for example, OPA192, below design file can be used for simulation to verify the functions etc. in TINA program which can be download from 2nd link:

    www.ti.com/.../getliterature.tsp

    http://www.ti.com/tool/tina-ti

    I will send you an email and loop our delta-sigma ADC expert about your question of driving a delta-sigma ADC.

    Thanks.

    Best regards

    Dale