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Original question:

ADS131M08: Data rate

ADS131M08: Overall accuracy 4-20mA loop

Theo Keinarth
Intellectual 325 points
Part Number: ADS131M08
Other Parts Discussed in Thread: OPA2992, TPS7A20, LP2985A

Tool/software:

Hi Ti-Team

I have an additional question regarding my circuit with the ADS131M08.

I tested everything so far with the EVM board I have an everything looks fine. At least at room temperature. I will perform a 2-point calibration at 4ma and 20mA in our final product.

My questions are:

How accurate will these values be after 10/20 years?
Can I achieve 0.1% overall accuracy over a temperature range from 0-60°C with the internal reference?
Is the input bias current (3-4µA) about to change with time and if so should I use input buffer (e.g. OPA2992)?
Is the LP2985A (new version) good enough for 0.1% or should I use the TPS7A20?

Thank you in advance.

Regards Theo

  • +1
    TI__Mastermind 45805 points

    Hi Theo,

    The error or accuracy is determined by the combination of all factors on a system level, not only the errors from the ADC, but also the errors or noise from the circuit and PCB layout. The ADS131M08 datasheet has specified the specifications at room temperature, and also the drift (for example, gain/offset error drift, long-term gain/internal Vref drift and so on). It is good to see you are planning to use a LDO for the ADC, but the PSRR of the LP2985A LDO is not too high, it depends on whether your power supply is clean or not. It is hard to say whether one of the factors can guarantee the desired 0.1% accuracy or not because the accuracy is the combinations of all error sources on the system level.

    TI provides a online calculator tool below that can help you estimate the TUE (total unadjusted error) as a start point:

    https://dev.ti.com/gallery/view/PADC/PADC_Design_Calculator_Tool/ver/1.29.0/?device=ADS131M08

    BR,

    Dale