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Request for TI part suggestion_4-20mA DAC

Namratha P
Prodigy 60 points
Other Parts Discussed in Thread: DAC161S997, TIDA-01504, DAC161P997, DAC8830, DAC8740H

Hi Team,

We have current project specifications as in the attached PPT attached herewith. We  have started the project .We  have to narrow down to suitable solution.

we need solutions for this requirement. Please suggest and help us to find proper solutions Metering application specifications.ppt

  • 0
    TI__Expert 5820 points
    Hi Namratha,

    I have a few questions to help me better understand your proposed design and recommend an appropriate DAC.

    1. Are you using a two or three wire design for your two current outputs?

    2. You provided a resolution requirement. What is your error specification requirement and over what temperature range?

    3. Can you elaborate on the isolation requirement?

    4. What is meant by 'time constant selectable'? Is this a setting time requirement?

    Thanks,
    Garrett
  • 0 in reply to Garrett Satterfield
    Prodigy 60 points

    Hi Garrett,

    Please find answers below.

    1. Are you using a two or three wire design for your two current outputs?

    - We are using 2 wire current outputs

    2.You provided a resolution requirement. What is your error specification requirement and over what temperature range?

    - Total unadjusted error (TUE): 0.05% maximum & Temperature- -40 -+85 deg

    3. Can you elaborate on the isolation requirement?

    - We need galvanic isolation

    4. What is meant by 'time constant selectable'? Is this a setting time requirement?  

    - This is for loop current slew rate control. This is helpful in controlling rate of change of loop current by controlling time constant.

  • 0 in reply to Namratha P
    TI__Expert 5820 points

    Hi Namratha,

    The only fully integrated two wire current loop devices we have are DAC161S997 and DAC161P997. These devices would not meet your error specification. An error specification of 0.05% over temperature is difficult to achieve and calibration over temperature will likely be required. I would recommend looking into the discrete solution offered in TIDA-01504:

    https://www.ti.com/tool/TIDA-01504

    This reference design uses the highly accurate DAC8830 with minimal temperature drift. With calibration, a design like this may suite your needs.

    As for the isolation, I am not sure how you would implement the isolation mid current loop like your block diagram shows. Are you sure this is the requirement? I have seen isolation effectively between the microcontroller and other sensing circuitry but not mid loop. Let me know if you have more information on this.

    Thanks,
    Garrett

  • 0 in reply to Garrett Satterfield
    Prodigy 60 points
    Hi Garrett,
    Thanks for the reply.
    I have another query.
    Could you please suggest me a ADC with 4-20mA input with HART complaint
    Thanks,
    Namratha
  • 0 in reply to Namratha P
    TI__Expert 5820 points

    Hi Namratha,

    The ADC on the input module is not HART compliant itself. The ADC is used simply to digitize the voltage at the load resistor. The current in the loop is then calculated from this voltage. A HART modem is required for HART communication. I have attached a diagram illustrating this below. The DAC8740H is a HART modem used for HART communication. As for selecting a particular ADC I would recommend posting to the ADC forum to learn more about the requirements for this application.

    Thanks

    Garrett