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DAC161S997: connect multiple analog outputs

Marcos Torres1
Prodigy 10 points
Part Number: DAC161S997
Other Parts Discussed in Thread: DAC8750, DAC8775, DAC8760

Hi all

We are making a PLC with several I/O and the analogs outputs are driven by the DAC161S997

The problem is the connection of these outputs, we are using a 24VDC power supply to power the loop, and a 3.3VDC to power the digital side. These two have a common ground, so when we connect the loop supply, the DAC gets hot and the current in the loop goes to 40 mA.

To avoid this, we separated the grounds so the 24VDC runs alone in the loop and the 3.3V powers the DAC.

We observed this was the only way the DAC worked properly.

But when we connect a 24VDC actuator, it doesn't work because this one connects internally the 4-20mA input ground to the 24VDC supply (as expected)

Another Issue we have is to connect multiple DACs, we have 4 analog outputs and we only can use 1. Since we have only one 24VDC power supply we cannot connect the 4-20ma loops in paralell because when we make the ground common the DACs won't work properly.

So, if we want to work we these outputs we need to have one 24VDC supply separately from each loop and at the same time the power in the loop cannot be common with the 3.3V DAC supply, A real nightmare!

We have rechecked the connection several times and it is the same provided in the datasheet:


I appreciate any help with this, we have tested everything with the same result.

Thanks

  • 0
    TI__Genius 11750 points

    Howdy Marcus,

    Thanks for posting and welcome to the e2e forums! I have an idea that you may require a different type of device to drive the actuator you've described, as the DAC161S997 is generally a great candidate when developing a sensor/field transmitter that (both) obtains power and reports current on the same loop.  As you've noticed, the device generates it's own local ground, which should not connect to LOOP-, or any other generated ground.  Additionally, you will require a separate power source for each device to accurately report and modulate current. 

    The DAC161S997 is generally used in two-wire applications (one current loop), however, you will require a device that has two independent current loops.  One loop that is responsible for modulating the 4-20mA current, and another loop that provides power to the device.  With this type of device you will be able to share one power source for multiple devices.

    A small subset of these devices include the DAC8760, DAC8750, DAC8775.  If you let me know the specifics of the required current range, resolution, and supply rail I will be able to make some recommendations. I've also listed a couple of TI Designs that I believe you will find useful in your efforts in building your application circuit.  Please let me know if you find the links useful, and please don't hesitate to ask any questions about the material.

    Best Regards,

    Matt