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DAC7760: Output as fault indicator

Nam, Dino
Expert 5995 points
Part Number: DAC7760
Other Parts Discussed in Thread: , DAC7750, DAC8775

Dear team, 

My customer would like to use 0~10V output and 4 to 20mA as dual output mode. 

The question from customer is like below. 

If the fault status like over range status happens, they would like to send to output 11V on voltage output and 24mA on current output at the same time. 

Is it available? 

Please let me know your opinion. 

Thank you. 

  • 0
    TI__Guru* 93115 points

    Dino,

    First, if the customer wants to set some sort of fault status, this device does not have any fault detection for itself.

    As for setting the DAC to 11V and 24mA output "at the same time", I think that the DAC7760 can do this, but it requires setting several registers for this operation.

    First the DAC7760 would be operating in dual-output mode by setting the DUAL_OUTEN in the configuration register. To set the voltage and current levels to the fault level, it would also require the OVR bit to be set so that the voltage range could go to +11V and the IOUT range would need to be set to 0-24mA. The outputs should go to 11V and 24mA with a DAC code of 0xFFF. Once the fault indication is done, the OVR bit would need to be reset back to 0 and the current output range would need to be set back to 4-20mA. 

    If there are any questions about it, I would highly recommend getting a DAC7760EVM to verify the output and the settings on the device to test it.

    Joseph Wu

  • 0 in reply to Joseph Wu
    TI__Expert 5995 points

    Hello Joseph, 

    Thank you for your suggestion. 

    I have one more question, Under dual-output mode condition, 

    If the customer would like to calibrate current and voltage output separately, Is there any way? 

    For example, Under dual-output mode condition, current output is correct but voltage output is needed calibration, Is there any way to correct only voltage output? 

    If not, Is there other device that can control voltage and current output separately?

    Thank you.  

  • +1 in reply to Nam, Dino
    TI__Guru* 93115 points

    Dino,

    This device cannot control the output of the current and voltage separately. There are calibration registers for both the gain and the offset. However, these control a single DAC that then has a voltage output and a current output. These outputs cannot be calibrated separately. 

    I don't know of any devices that can control the voltage separately at exactly the same time. One possibility would be using multiple devices (one to control the current and another to control the voltage. If you wanted to control them at the same time, then you would need two SPI compatible channels to write to the devices and control them at the same time. You could do this with two DAC7760s (or one DAC7760 and a DAC7750).

    Another possibility would be to use the four-channel DAC8775 and use one channel for voltage and another for current. Each channel is controlled independently. However with one device, you would only be able to write to each channel individually. For example, if you were in some alarm condition, you would set the output of one channel to 11V and then you would set the output for other channel to an 24mA. They would be written to in consecutive writes, and not executed at the same time.

    Joseph Wu