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DAC161P997: Giving Fix Current output 11.8 mA with Zero DAC Code and 14.6mA output with any DAC Code Other than Zero(Between 0 and 65535)

Karan Thawani
Prodigy 50 points
Part Number: DAC161P997

Hello Everyone,

I hope you all are fine and doing well. I am planning to use DAC161P997 in one of my design to produce accurate 4-20mA output. I have used the same reference circuit given in the datasheet. But it is giving Fix Current output 11.8 mA with Zero DAC Code and 14.6mA output with any DAC Code Other than Zero(Between 0 and 65535). Below are some key points which I have observed.

1. My Digital communication seems ok as I am sending DAC Code every 500ms and I am observing High to Low transition on Ack Pin after the end of frame of each DAC Code.

2. Also There is no error(Error Pin is always high).

3. The loop also seems ok as I am getting -600mV across the Out Pin of DAC and (COMA/COMD).

Please suggest what other things may be there which I am missing.

Best Regards,

Karan Thawani

  • 0
    TI__Guru* 93715 points

    Karan,


    Just to be sure, do you have complete circuit? I'm assuming that you created something similar to the typical application shown on page 26. Is there anything else that is connected to the circuit? Anything connected to the output of the TPS79801? If there are any other circuits connected, there may be extra current greater than the 4mA that can be pulled from LOOP+.

    I would start by making some measurements around the circuit. After your startup, I would guess that you would expect a current of 4mA being pulled from LOOP+. At that point, I would measure the voltages from BASE to GND and LOOP- to GND (you can throw in LOOP+ to GND as well). These measurements check to see that the control loop is working (or at least is in a position to set the current).

    I would also measure the current going through the transistor. You can do this by measuring voltage across the 22Ω resistor. I would also measure the current going into the TPS79801 and that can be measured from the 100Ω resistor.

    Check these measurements and let me know what you get.


    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 50 points

    Hi,

    Thank you so much for your inputs. I checked with your points. Actually my 3.3 LDO was taking huge current thats why DAC was not able to regulate the current. By replacing LDO now circuit is working fine. Thank you so much.