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DAC161S997: 4-20mA current output (DAC161S997) and digital output (16-30V) share the same two terminals, which output mode selected leave to user, any ideas or solution available?

Dawei
Intellectual 280 points
Part Number: DAC161S997

4-20mA current output (DAC161S997) and digital output (16-30V) share the same two terminals, which output mode selected leave to user, any ideas or solution available?

The blue block indicated in the picture below maybe some analog switch or mux which should has TTL or CMOS control signal, it is my current thought, any other ideas or solutions?

  • 0
    TI__Mastermind 46290 points
    Hello,

    The image you posted did not make ti through. I am also not totally clear on what you are asking. Can you please try to repost the image along with some elaboration on what you are attempting to achieve?
  • 0 in reply to Kevin Duke
    Intellectual 280 points

    Kevin,

    Can you get the picture now?

    My circuits requirements,

    1, 4-20mA current output (external max 42V power supply); 2, Digital output (0-10KHz, 16-30V external supply range); 3, We want to map AO and DO to the same terminals and which one output is software selectable.

    My current thougt is to seek some analog switch or FET switch for the requirements above.

    Regards,

    Ma Dawei

  • 0 in reply to Dawei
    TI__Expert 5820 points
    Hello,

    From the 4-20mA loop with DAC161S997 I don't see any issue with having switches on LOOP+ and LOOP- to connect/disconnect from a terminal block. Even if the switches add series resistance the device will not have an issue regulating the loop current. Will DAC161S997 be powered when the digital output is active? If so, some current can flow through the BJT as the output amplifier tries to drive the current even though the loop is disconnected.

    I am not quite sure of the nature of the digital circuit you have shown. Will this also be loop-powered?

    Thanks,
    Garrett
  • 0 in reply to Garrett Satterfield
    TI__Expert 5820 points
    Hello,

    Any update on this thread?

    Thanks,
    Garrett
  • 0 in reply to Garrett Satterfield
    Intellectual 280 points

    Garrett,

    I will use a local power supply to feed DAC and the drive of digital output, loop power will not be used. The snap is from the data sheet of DAC161S997, I forget to modify it by deleting LDO.

    Digital output is pulse output, from 0 to 10kHz and external pull up to 16VDC to 30VDC, one BJT with open collector will be used behind opto-coupler.

    Do you want to close this thread now? I still need to find the switch used in diagram above.

    Regards,

    Ma Dawei

  • 0 in reply to Dawei
    TI__Expert 5820 points
    Hi Ma,

    Understood, the series switch should not cause any issue with the analog 4-20mA signal as long as Ron is reasonably low. I do not have a particular recommendation for these switches but perhaps you could post to the switches & multiplexers forum for a recommendation or use the parametric search tool.

    Thanks,
    Garrett