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DAC161S997: Using two DAC161S997 for 4-20 mA output transmission

Jesus Ortiz
Prodigy 10 points
Part Number: DAC161S997

Tool/software:

Hi, I have read several threads about the problems you may have when using two DAC161S997 in the same circuit sharing any of the loop lines. 

In my case, I have the circuit below, for transmitting pH and electrical conductivity. There are two DACs powered by independent LDOs. Each loop in independent from the other (looop lines are not shared), but GND net is shared by the two circuits and I'm not sure if that point may cause any issue.

I'd appreciate your advice on whether the circuit is correct or whether I should make any changes before launching prototype production.

Thanks in advance

Jesús O.

  • 0
    TI__Guru* 96175 points

    Jesús,


    In general, this looks ok to me. The one thing to keep in mind for multiple DAC161S997 devices is to make sure that the OUT pin for both devices are independent from each other. The voltage of OUT below ground actually controls the current through the device's loop.

    In your circuit, the only way this is a problem is the loop power supplies (the 6V to 28V terminals on the right). These supplies must be completely independent and have no common voltage. They must be isolated supplies.

    Other than that, I don't see any other connection between the OUT pin between the two devices.


    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 10 points

    Hi Joseph,

    Thanks for your reply. The loop power supplies are completely independent and have no common voltage. That's for sure.

    So, GND being shared by the two DAC161S997 devices is not really an issue? In my circuit, GND is common to the microcontroller (SPI bus) and DACs, but loop power supplies are independent and isolated. I though that sharing GND could be a problem, but I'm happy to read your answer. I am quite concerned about this matter and I want to be sure before going ahead with production.

    Regards

  • 0 in reply to Jesus Ortiz
    TI__Guru* 96175 points

    Jesús,

     

    Yes, I don't think sharing a ground is a problem. Again, the OUT pin for the devices must be independent because that's the voltage node that controls the loop current. 

    If you wanted to test this, I think you could put together two DAC161S997EVMs and run them independently.

    Joseph Wu