Hello Joseph Wu, I hope this message finds you well. I have drawn a block diagram to illustrate my intended design. The original DAC chip was meant for a 2-wire setup, where the loop power supply is located externally. However, what I want to do is use a DC-DC converter on my own board to create an independent power source and supply the loop power directly, so that external devices (such as PLCs) only need a resistor and a receiver circuit to read the current—no additional power supply required. Is this what you would call a 4-wire design? Under this approach, the negative output (-Vout) of the DC-DC converter is routed externally through the LOOP+ terminal, while the DAC’s OUT pin serves as LOOP-. This line connects through the external resistor (for example, 250 Ω) in parallel at the external device, then returns via the loop wiring, passes through the DAC’s internal 40 Ω resistor, and finally arrives at COMA and COMD. In other words, the connection sequence is: DC-DC (-Vout) → external resistor (e.g., 250 Ω) → DAC OUT → internal 40 Ω resistor → COMA/COMD The key idea is that the loop is fully powered from my board, eliminating the need for an external power supply. All the external device needs is a resistor and a receiver (ADC) to measure the current. I look forward to hearing your thoughts or any feedback you might have.
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