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I need some good suggestion to choose the most suitable a/d converter for new project

PAOLO BOZZOLA
Intellectual 255 points
Other Parts Discussed in Thread: ADS8688, ADS8678, ADS8668

Dear All,

I have to start a new project where the specs are the following:

  1. 16 differential channels
  2. resolution 12 or 14 bits (16 can be ok also)
  3. SAR ADC can be ok
  4. Max sampling rate: 500ks/S guaranteed
  5. Input ranges:
    1. +/-10V
    2. 0~+10V
    3. +/-5V
    4. 0~+5V
  6. (external op-amp solution can be accepted of course, in order to accomplish the input ranges, with preset by jumpers for each channel)
  7. possibly self-calibration
  8. i2C or SPI interface

Basically this new circuit should replace the Analog Inputs of 2x National Instruments NI6024 DAQ boards.

I have used a lot of different TI solution in my past projects, all with success; this time I would be more happy to collect first some hints from designers who already have made a similar choice before.

Thanks so much for the help

  • 0
    TI__Mastermind 45215 points

    Hi Paolo,

    Thanks for your information. Are you looking for differential input ADC? If single-end input can be accepted, ADS8688 family is a prefect solution for you. Key features:    Bipolar direct input can support your all ranges and no external active component is needed, Maximum throughput is 500ksps, SPI interface SAR ADC with higher precision performance.

    ADS8688:  8ch, 16bit

    ADS8678:  8ch, 14bit

    ADS8668:  8ch, 12bit

    Please go to this link to check the datasheet, and let us know if you have more questions, thanks.

    http://www.ti.com/product/ads8688

    Best regards

    Dale Li

  • 0 in reply to Dale Li
    Intellectual 255 points
    Dear Dale,

    thanks for the suggestion, I also had this device in my target, but I need some tips before confirming the choice.

    Here are some questions, if you are so kind to clarify me:

    >1) each AIN_xGND must be tied to the analog ground, correct?

    >) then any pin AIN_xP can accept any voltage of such ranges: ±10.24 V, ±5.12 V, ±2.56 V, ±1.28 V, ±0.64 V 10.24 V, 5.12 V, 2.56 V, 1.28 V depending on iternal register configuration: correct?

    >3) since I need to manage both bipolar inputs (+/-10V typ) or unipolar (0~+10V typ) or even 0~20mA or 4~20mA, sure I need a front-end circuitry for each AIN channel, based on a suitable OP-AMP.
    In this case a rail-to-rail OP-AMP powered by +/-10V or even +/-15V could be a reasonable choice? Which cheap good op-amp do you suggest to match my needs and setup a stable front-end for each AIN input?

    Thanks so much and my best regards

    Paolo
  • 0 in reply to PAOLO BOZZOLA
    TI__Mastermind 45215 points

    Hi Paols,

    Thanks for oyur feedback.

    1) Yes, balanced input is recommended, please refer to Figure 95 in datasheet.

    2) Yes.

    3) I'm trying to understand what you mean "manage", will your signals switch among these different signals on the same channel? actually, ADS8688's input range can be modified at any time also different channels can have different input ranges, they are independent.

    Best regards

    Dale