The recommended calibration procedure
is as follows:
- Preset the offset and gain
calibration registers to 000000h and 400000h, respectively.
- Perform offset calibration by shorting the inputs using the
input multiplexer. To include the offset error of the external amplifier stages,
short the inputs of the system. Acquire conversion data from the channel and
write the average value of the data to the offset calibration registers.
Averaging the data reduces conversion noise to improve calibration
accuracy.
- Perform gain calibration by applying a calibration signal to
the inputs. To include the gain error of the external amplifier stage, apply the
signal to the system inputs. For standard input range mode, choose the
calibration voltage to be less than the full-scale input range to avoid clipping
the output code. Clipped output codes result in inaccurate calibration. For
example, use a 3.9V calibration signal with VREF = 4.096V. When
operating in extended range mode, a calibration signal equivalent to
VREF does not cause clipped output codes. Acquire conversion data
from the channel and average the results. Use Equation 21 to calculate the gain calibration value.
Equation 21. Gain
Calibration Value = (expected output code / actual output code) ·
400000h
For example, the expected output code of a 3.9V calibration voltage using a
4.096V reference voltage is: (3.9V / 4.096V) · 7FFFFFh = 79E000h.