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ADS1248: Recommendation INA device

Takumi Suzuki1
Mastermind 8680 points

Part Number: ADS1248
Other Parts Discussed in Thread: INA129, ADS124S08

Hi,

My customer plans to use INA129 in front of ADS1248.

Will you advise me the device that is better than INA129 for ADS1248?

And will you also provide me the reference circuit with using your recommendation device, if possible?

Thanks!

Best Regards,

  • 0
    TI__Guru** 101185 points
    Takumi-san,


    This question requires a bit more information. The ADS1248 already provides a PGA, which is very close in operation to an INA. The amplifier construction and gain setting are done exactly the same as in a regular instrumenation amplifier. If they are unable to use the PGA, or if it isn't sufficient, then it would be helpful to know why they cannot use the PGA.

    Can I get more about the customers application, and how they plan to use the INA129? Why can't they use the PGA? I'd like as much detail as you can provide.


    Joseph Wu
  • 0 in reply to Joseph Wu
    Mastermind 8680 points

    Hi Joseph-san,

    Thank you for your reply.

    The application is "RTD" and "Thermocouple".

    The customer would like to get at least 16bit ENOB (peak-to-peak noise) at 128 gain with 40/80SPS. (AVDD=5V, AVSS=0V, ref=2.048V)

    So they plan to use INA129 in front of ADS1248.

    If I misunderstand about ENOB, please let me know.

    Best Regards,

  • 0 in reply to Takumi Suzuki1
    TI__Guru** 101185 points
    Takumi-san,


    For the RTD application, it is very unlikely that a gain of 128 would be required. For the thermocouple, high gain is very likely. However, thermocouple accuracy is lower than that of the RTD, so I would question if that kind of noise performance is required.

    The ADS1248 in PGA of 128 won't get 16 bit ENOB for a higher data rate like 40SPS and 80SPS. With the INA in high gain, the noise would be about 200nVpp and that is without considering the ADC noise. I think it is possible to do get to 16 bits, but might be a bit difficult to construct.

    Instead, I would consider using the ADS124S08. With the sinc3 filter, the noise performance is 16 bits all the way out to 100SPS. Again, it doesn't include 50/60Hz noise rejection, but it does allow for a simpler circuit. Note that a sinc3 filter does have some latency, and getting a sample may take longer.


    Joseph Wu
  • 0 in reply to Joseph Wu
    Mastermind 8680 points
    Joseph-san,
    Thank you for your advice.
    I will ask the customer.
    Best Regards,