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High performance ADC for DC measurement

Kim Lorentz
Prodigy 50 points
Other Parts Discussed in Thread: ADS8694, ADS1291, ADS1282-SP, ADS1262, ADS1220, PGA280, ADS1259, ADS1282, REF5025, OPA1632

I am making myself a DC digital voltmeter and are looking for a good ADC to do that. What is an good ADC to do this work?

I think I am going to use an Delta-sigma ADC for dc volt measurements. And I need to measure +/- voltage.

These are the ones I am looking at:

  • ADS8694 - 18-bit
  • ADS1291 - 24-bit
  • ADS1282-SP - 31-bit
  • or something like this

I am using and Intel Edison to do the work, Its going to be battery powered.

I have access to National Instrument measurement equipment for testing. The system can measure with 24-bit resolution.

  • 0
    TI__Guru* 94415 points
    Kim,


    There are quite a few devices that could be used. I'd consider using something similar to an ADS1220 (24 bit), or if you need more resolution, maybe an ADS1262.

    What sort of input range do you need? With all of these ADCs, the inputs need to be within the range of the ADC (which is often within the supply range. What accuracy are you looking for? What data rate do you need?


    Joseph Wu
  • 0 in reply to Joseph Wu
    Prodigy 50 points

    I need to be able to read DC volt:

    • +/- 100mV,1V,10V
    • 0-100mV, 0-1V, 0-10V, 0-30v, 0-60V (voltage above 10v can be read true external PGA or divide voltage by resistors and amplifier)

    Need 24 to 32-bit. The speed is only 100 sps max, its needed for high accuracy readings not speed.

    For AC readings I only need 16 to 20-bit. But high speed for readings signals up to 100Khz and max 10v.

  • 0 in reply to Kim Lorentz
    TI__Guru* 94415 points
    Kim,


    You might be able to use something like a PGA280 in front to give you some added range (most 24-bit ADCs operate from 0 to 5V or ±2.5V. The PGA280 does operate off of ±15V supplies and is used as a a front-end for ADCs.

    If you're interested, there is an evaluation module for the ADS1259 and PGA280 which might work for you.

    www.ti.com/.../ads1259evm-pdk


    Joseph Wu
  • 0 in reply to Joseph Wu
    Prodigy 50 points

    What about an ADS1282-SP. EVM board

    I can use AIN1 for volt dc and AIN2 for amp dc.

    And use PGA280 or equal to adjust the output down to +/- 2.5v

  • 0 in reply to Kim Lorentz
    TI__Guru* 94415 points
    Kim,


    I think this could be done with the ADS1282, however, I think the ADS1259 is a bit simpler.

    The ADS1282 has a digital filter that has a latency that extends 62 data samples. That means if something changes on the input, the data doesn't reflect this change for the next 62 data. While the digital filter has a nice flat passband, you probably don't need this in a voltmeter. The ADS1282, is also more expensive.

    In comparison, the ADS1259 is a bit simpler. It has a good noise performance, and the digital filter settles in on sample. It's also significantly cheaper than the ADS1282. It also has an internal reference (you'll have to decide if the reference performance is good enough for your application.


    Joseph Wu
  • 0 in reply to Joseph Wu
    Prodigy 50 points

    I found the price of the ADS1282 and ADS1259.

    I am going for the ADS1259 and are working on creating an bipolar connection circuit to be able to measure +/- voltage and not only 0 to X voltage.

    For analog power supply I am using

    • TPS72325DBV - minus 2.5vdc
    • TPS79225DBV - plus 2.5vdc

    For external Ref. voltage I am wondering if I need one plus 2.5v and one minus 2.5v?

    • REF5025 - High Grade 0.05% 3ppm/C, plus 2.50vdc

    I am also using an PGA280IPW (ADS1259EVM Board) or/and an OPA1632(High-Performance, Fully-Differential Audio Operational Amplifier)

  • 0 in reply to Kim Lorentz
    TI__Guru* 94415 points
    Kim,


    I've never used the TPS72325 and the TPS79225, but I don't foresee any issue with them.

    You will only need one reference.

    I would note that most of what you are describing is already similar to the ADS1259EVM, which you might want to get to play around with the functions on the device. Even if you don't you can download the user manual and look at the schematics and layout just in case you need some sort of template to work from.


    Joseph Wu