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DAC8750: DAC8750 Calibration below 4mA

Melissa Wetter
Prodigy 90 points
Part Number: DAC8750

Hello,

after working with the DAC8750 for a while I encountered a problem.

The DAC is in the 4-20mA mode with the Output set to 0x0000 (should be 4 mA) but it's 4.23mA.

If the DAC is below 4 mA, like 3.98mA,  I already adjusted the output successfully.

But what can I do if it's over 4mA.  I think the Zero Calibration Register cannot reduce the output?

If it's set to 0 the output is above 4mA. If I reduce or increase the value of the Gain/Zero Calibration the output at 0x0000 is still 4.23mA.

Thank you very much

  • 0
    TI__Guru 53333 points

    Hi Melissa,

    You are correct, the offset and gain calibration is only a digital calibration.  The DAC itself cannot output lower than its 0x0000 code.  If you look at the transfer function, you will see that the offset error is reduced until you get to the point where the ideal DAC would output 4.23mA.  This is the difference between zero-scale error and offset error.   

    One workaround would be to operate in the 0-20mA or 0-24mA range so that you have more headroom/footroom for the offset calibration.

    Thanks,

    Paul