DAC161P997: DAC161P997: 0-20 mA DC output

Chinmay,

I can see how you can get the current output for this device (as a current control from the loop voltage). However, I can't see how you want to set the voltage output.

For the true zero output, how far off from zero current are you? There is some amount of current needed to control the loop, so you cannot get down to exactly 0V. In the specification table, you'll see this for the loop current output:

That means that you'll need a minimum of 180uA of current for the loop.

Joseph Wu

Joseph,

As you can see I have used 2 position DIP switch (JP1)

a) Position 1 --> 499 Ohm Loop Termination Resistor for 10V Output

b) Position 2 --> 249 Ohm Loop Termination Resistor for 5V Output

Chinmay

Chinmay,

I can see the connection to the switch, however the connection to the terminal is still to the supply. In the schematic, the positive terminal is connected to the +15V and the negative terminal is connected to the ground (+15V ground). Across the terminal, you'll always see +15V. For the DAC161P997, the control will always pull current directly from the +15V supply through the NPN. In that case, the controlled current never reaches the terminals.

Where are you measuring the current for the loop? Are you measuring through R16? What was the true zero amplitude that you were measuring?

Joseph Wu

Joseph,

I have fixed my schematic, thanks for your inputs.

Chinmay

Chinmay,

Ok, I can see that the switch close can lead to the voltage outputs. With the switches open, you could insert a sense resistor to allow current to flow.

As I mentioned in the previous post, the current range doesn't really extend to 0mA, and there's a small offset of 180uA near 0. What are you measuring? Can you set the code through the range of operation and plot the current output? With the 4-20mA range, I would expect the output to be linear through the entire range.

Is this a circuit you've already constructed? Have you used the DAC161S997EVM to play with a similar circuit?

Joseph Wu

Joseph,

I am building a breakout PCB for DAC161S997.

I will update you after I play with the DAC161S997 hardware.

Chinmay

Chinmay,

Ok, I can leave this thread open. Let me know if you have any questions about the DAC161S997 when you get your board back.

Joseph Wu