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DAC161S997: Loop Error occurs at large DAC outputsignal jumps

Sarah Mazenauer
Prodigy 10 points
Part Number: DAC161S997

Hi,

We use the DAC161S997 for our 4 - 20mA pressure transmitter.

Now we have the problem, that if we use a high load resistor (510R) and a supply voltage of 24V, The DAC goes straight to loop error when we send as first DAC setting a value close to DAC-MAX (0xfff). The only work around we found till now is, to step up tu the DAC_MAX value with 4 to 5 steps. Is our problem known? Have you other possibilities to prevent the DAC from going to error loop? (Not to reduce the load resistor).

Kind regards sarah

  • 0
    TI__Guru* 93425 points

    Sarah,


    The ERRB is set off from a loop error whenever the device can't sustain the required output current. The datasheet says this is often from a drop in loop supply or an increase in the load impedance. From a circuit standpoint, the op amp that controls the loop current has a feedback. When the feedback is lost, the circuit senses it and sets the error condition.

    I'm not aware of anything that would specifically be a problem with a larger load resistor, except maybe that the circuit doesn't work at low enough voltage. When supply is 24V and the loop current is 25mA, the 510Ω resistor drops 12.75V. At that point, the circuit needs to work off of 11.25V. Does the circuit work at that low of a voltage without the load resistor? Does it work at 10V?

    If you're able to step into the max current with 4 to 5 steps, but not able to go from a straight low to a high setting, this might be something similar to a slewing condition. I might try slowing down the loop a little. For this, you might try changing the C1-C3 values to something a little higher just to test it.

    I'm not sure if this would cause an ERRB trigger, but another possibility is that the circuit might be a bit unstable. Do you have anything connected to the circuit ground? This is the ground of the DAC161S997 connected to anything (capacitance to the loop or scope probe connection)? Capacitive coupling from the ground to the loop might cause the circuit to lose stability. With a reduced stability, a large change in the loop current might cause a large overshoot that causes this type of error.

    Are you able to share a schematic?


    Joseph Wu