Hi,
Good Day. I have a customer who is working with DAC16S997. Please see below his query for your reference. Thank you very much.
I was looking for some info on how I can use the DAC161S997 in loop powered 3 wire mode. The available info is for 2 wire 4-20mA transmitter and self powered. What about the loop powered 3-wire transmitter
Best Regards,
Ray Vincent
Ray,
We don't have any examples showing the DAC161S977 in a 3-wire transmitter. Generally, the DAC161S997 is suited to 2-wire transmitter applications where the device is powered by the loop.
A three-wire transmitter has some shared power and ground connection and then a signal return that transmits the current from the loop. In that configuration, the supply voltage is separate from the loop.
The way that the DAC161S997 is set up, the device controls the total loop current through the drive of the BJT from BASE as shown in the example in the datasheet:
The BJT sets the current going through COMA to OUT. Because of this, the OUT pin voltage will be negative with respect to the ground connection. The device is powered by the loop, and the total current of the LOOP will be the same as the transmitter. This is how the DAC161S997 works as a 2-wire transmitter.
A standard current output DAC would be better suited for a 3-wire transmitter. In that case, the power and ground come from a supply, and a current can be directly output. The DAC8750 or the current output setting from the DAC8771 would be proper choices for that application.
Joseph Wu
