• State Resolved
  • Locked Locked
  • Replies 8 replies
  • Answers 2 answers
  • Subscribers 46 subscribers
  • Views 1259 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DAC161S997: Typical application for 4-20mA output

Zhongwen Jin
Intellectual 385 points
Part Number: DAC161S997
Other Parts Discussed in Thread: DAC8771, DAC8760, DAC8750, DAC7750

Use local power supply, and only the OUT pin for 4-20mA output.

What is the typical application circuit please? 

In the datasheet, it shows the application for loop. Can I just use OUT pin and GND for 4-20mA output?

  • 0
    TI__Expert 5820 points

    Hi Zhongwen,

    The DAC161S997 is a 2-wire loop powered device. The signalling current and current to power the transmitter circuitry are combined. It sounds like you are looking for a 3-wire device to output the 4-20mA signal on a separate loop than the power supply. Refer to the blog below for an overview of 2-wire vs. 3-wire current loops.

    https://e2e.ti.com/blogs_/archives/b/precisionhub/archive/2014/04/29/industrial-dacs-an-overview-of-analog-outputs-and-architectures

    Some 3-wire device you can look into are the DAC8760 and the DAC8771.

    Let me know if you have follow up questions.

    Thanks,

    Garrett

  • 0 in reply to Garrett Satterfield
    Intellectual 385 points

    Thank you very much, Garrett

    In the link of you provided, my application is more like Figure 3.

    We only need to generate 4-20mA output to load. Can we still use DAC161S997 to achieve this please?

    Thanks and kind regards

  • 0 in reply to Zhongwen Jin
    TI__Expert 5820 points
    Hi Zhongwen,

    Not if your application is like Figure 3 where the power supply is separate from the current loop. DAC161S997 will require a series supply. DAC8760 and DAC8771 are devices that will provide a current loop as shown in Figure 3. We have many reference designs with these devices if you search our reference design page. You can also order the EVMs to test the devices in your application.

    Thanks,
    Garrett
  • 0 in reply to Garrett Satterfield
    Intellectual 385 points

     DAC161S997 has got a good output current out of range error reporting. That is the main reason we pick it, and we have got its demo board. Probably we can try it out on the demo board. If it works, I will be wondering why TI does not put this application in the datasheet.

  • 0 in reply to Garrett Satterfield
    Intellectual 385 points
    Hi Garrett. You are right. We have tried our application on the demo board DAC161S997. It is not working! I think it is only for 2-wire current output.
    I have checked the two options you recommended, have you got a cheaper solution than those. We only need 4-20mA current output. We do not need voltage output etc.

    Thanks and kind regards,
  • 0 in reply to Zhongwen Jin
    TI__Expert 5820 points

    Hi Zhongwen,

    It should work if you use and LDO to provide VA from the loop power supply, but again this will be the loop powered configuration where the power supply is in series with the loop. You would not be able to have a separate loop driving just the load (without the series loop supply).

    Do you require 16 bit resolution in your application? If you are just looking for the current output DAC7750 and DAC8750 are similar devices that do not have the voltage output included. DAC7750 is 12-bit and DAC8750 is 16-bit.

    You could also implement the circuit with one of our XTR devices and a discrete DAC. I have linked a reference design for this implementation below.

    http://www.ti.com/tool/TIDA-01536

    Yet another option is designing the circuit fully discretely by driving a high-side current source with a discrete DAC. Below is a reference design for a high-side V-to-I converter that could be designed for 4-20mA output and driven by a voltage output DAC to adjust the current loop.

    http://www.ti.com/tool/TIPD102

    Thanks,

    Garrett

  • 0 in reply to Garrett Satterfield
    Intellectual 385 points
    Very useful information. Thanks a lot for your help, Garret.
  • 0 in reply to Zhongwen Jin
    TI__Expert 5820 points
    Hi Zhongwen,

    No problem, let me know if you have additional questions after reviewing these design options.

    Thanks,
    Garrett