Hi,
According to equation (1) in data sheet P28, even if the full scale code FFF0h is set during unipolar output with the 0-5V range setting,
it does not seem to be 5V in the calculation.
Should I correct it by setting 8010h in the DAC gain calibration register?
Best regards,
Hi,
So the fullscale code for the 12-bit version of this device is 0xFFF, or 4095. But the 2^N value is 4096, so given that equation your FS values is:
VOUT(4095) = 5V × 1V/V × (4095/4096) = 4.99878V
I assume you are asking if you can ever actually achieve a true 5V output in the 5V range?
The short answer is NO.
This is really an architectural limit of all resistor-ladder DACs. Consider the R-2R architecture of a DAC:
This is the layout for a 4 bit DAC, but it is useful for this explanation. Note that even with all the switches connected to the reference code (full scale) the output is 4.6875V.
So even by increasing the number of switches, we are still limited.
The calibration function in this device is really just a digital calibration, meaning that your input code would be mathematically changed to add the offset and gain calibration, but the input of the DAC is still limited to the support input codes. If you truly require a 5V output, then you need to use a larger range (10V), and only operate the DAC to mid-scale. You could also use an external reference that is slightly larger than 5V.
Thanks,
Paul
