Hyejun, I'm still not sure how you intend on connecting this device. I generally see this device set up like a field transmitter (2-wire). It's basically like the diagram that you see in the data sheet: With the 2-wire transmitter you have a loop with a power supply and a transmitter that runs off of the loop power. There's a sense resistor near the supply that you would use to measure the loop current. This transmitter is remote and the DAC161S997 controls the current pulled through the loop. There's only the LOOP+ and the LOOP- and the DAC161S997 needs a variable ground for the COMA/COMD line. The COMA/COMD is not isolated from LOOP-, but needs to be able to float with respect to each other. This is important for the control of the current in the loop. In your case, you have a main power supply and it sets the power in the loop. If your circuit uses HART, I've seen DC-DC converters used for generating the supply for some controller used for programming a HART-enabled transmitter outside the normal loop. Regardless, I'm still unsure what you're trying to create. Can you please put up a basic block diagram of your circuit, and what you want to do? Joseph Wu
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