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DAC8760: bipolar Gain / Offset Calibration

Thomas Delfs
Prodigy 20 points
Part Number: DAC8760

In unipolar configuration the fixed point for gain calibration is the offset point (0000h).

In bipolar system regulary the offset point is in midscale (0V). For DAC8760 the offset at 0V is changed after Gain calibration.

  • 0
    TI__Intellectual 1570 points

    Hello Thomas,

    The digital calibration feature of the DAC8760 works by changing the code that is sent internally to the DAC. The gain calibration register allows the gain of the DAC code to be scaled from a range of 0.5 to 1.5 depending on the gain calibration data. The default value of the register is 0000h which corresponds to a gain of 0.5. To set the gain value to 1, write 8000h to the gain calibration register. With a gain value of 1, the mid-scale value for a bipolar output should still be at 0V. 

    For any other value, output of the DAC will correspond to the internal code sent to the DAC which is given by equation 6 in the datasheet. My recommendation is to use a combination of both user_gain & user_zero when calibration a bipolar DAC range to ensure that the mid-scale value still remains at 0V.

    Regards,

    Reza

  • 0 in reply to Reza Abdullah
    Prodigy 20 points

    DAC8760 is configurable as unipolar or bipolar system. I used the bipolar configuration and the User_GAIN shift the Offset in midscale.

    The 'fixed' offset point is at  '0000h' like unipolar system.

    I made some test's with a +/-10V configuration:

    If I change the User_GAIN the offset at 0V is shifted with ~35mV.

    At -10V it was 400µV

    Expected was something like the picture shows. The documentation of the DAC8760 is uncomplete.

  • 0 in reply to Thomas Delfs
    TI__Intellectual 1570 points

    Hello Thomas,

    Your observation is right. Since the DAC8760 calibration is purely digital, offset point is always fixed at code 0000h and not at 0V. With that said, you should still be able to digitally calibrate the DAC such that the error at 0V for a bipolar output range is corrected. For a bipolar range, you can assume that the gain error that needs to be calibrated is the half of the gain error for the full scale range. The offset error that needs to be calibrated will then be the error at mid-scale. Please let me know if you have issues achieving that result. 

    Thanks

    Reza