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DAC161S997: DAC

Anush Balraj
Prodigy 10 points

Part Number: DAC161S997
Other Parts Discussed in Thread: TIDA-00648, DAC8750, DAC8775, DAC8760

Hi Team, 

With reference to DAC161S997 picture shown below,

Here DAC will be powered from internal supply(Vlocal).We want to know what will be the voltage across LOOP+ and LOOP-.(This is not loop powered)

We understand that DAC will generate only current across LOOP+ and LOOP-.How about the voltage,Whether DAC will generate the voltage as well?

Since in this configuration other device will be connecting to LOOP+ and LOOP- and device expects power.

Please Clarify.

  • 0
    TI__Expert 5820 points

    Hi Anush,

    What do you mean that the device will be powered by an internal supply? The DAC161S997 is a loop powered device. A power supply needs to be connected across LOOP+ and LOOP- as shown in Figure 16 that you show.

    I am not understanding all of your questions. Can you provide a block diagram or more information to clarify what you are trying to accomplish? Perhaps there is a better device that will meet your needs.

    Thanks,

    Garrett

  • 0 in reply to Garrett Satterfield
    Prodigy 10 points

    Hi Garret,

    We are referring to TIDA-00648 reference design.

    There is provision to power the DAC with external power supply. And also to isolate the supply from the Loop power.

    In this J1  is the jumper which can be used to isolate the Loop supply. J6 and J5 are jumpers which will enable the external supply to

    the DAC.

    Now If we power the DAC through the external Supply,and loop is not powered(No power supply across LOOP+ and LOOP-) what will be the voltage

    across the LOOP+ and LOOP-? or only current will be generated from the DAC?

    Please clarify.

    Thanks

    Anush

  • 0 in reply to Anush Balraj
    TI__Expert 5820 points

    Hi Anush,

    The loop power supply is required for the device to regulate the loop current in this design. The analog signalling current cannot be produced from the external supply. The voltage across LOOP+ and LOOP- will be zero if no loop power supply is provided.

    DAC161S997 is considered a 2-wire analog output which requires the power supply and load resistor to be connected in series with the device. If the loop current is provided by an external power supply that is separate from analog signalling loop the device is considered a 3-wire analog output. See the link below for a comparison of 2-wire and 3-wire configurations.

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

    It sounds like you are looking for a 3-wire configuration in your application, since you are looking for a device that derives the loop current from an external power supply. For the 3-wire application you can use one of our 3-wire devices such as DAC8760, DAC8750, or DAC8775.

    Thanks,
    Garrett