Datasheet

AD7715
Rev. D | Page 18 of 40
CALIBRATION SEQUENCES
The AD7715 contains a number of calibration options as
outlined in Table 13. Table 23 summarizes the calibration types,
the operations involved and the duration of the operations.
There are two methods of determining the end of calibration.
The first is to monitor when
DRDY
returns low at the end of
the sequence.
DRDY
not only indicates when the sequence is
complete but also that the part has a valid new sample in its
data register. This valid new sample is the result of a normal
conversion which follows the calibration sequence. The second
method of determining when calibration is complete is to
monitor the MD1 and MD0 bits of the setup register. When
these bits return to 0, 0 following a calibration command, it
indicates that the calibration sequence is complete. This method
does not give any indication of there being a valid new result in
the data register. However, it gives an earlier indication than
DRDY
that calibration is complete. The duration to when the
mode bits (MD1 and MD0) return to 0, 0 represents the
duration of the calibration carried out. The sequence to when
DRDY
goes low also includes a normal conversion and a
pipeline delay, t
P
, to correctly scale the results of this first
conversion. t
P
will never exceed 2000 × t
CLK IN
. The time for both
methods is given in . Table 23
Table 23. Calibration Sequences
Calibration Type MD1, MD0 Calibration Sequence Duration to Mode Bits
Duration to
DRDY
Self Calibration 0, 1 Internal ZS Cal @ Selected Gain + 6 × 1/Output Rate 9 ×1/Output Rate + t
P
Internal FS Cal @ Selected Gain
ZS System Calibration 1, 0 ZS Cal on AIN @ Selected Gain 3 × 1/Output Rate 4 × 1/Output Rate + t
P
FS System Calibration 1, 1 FS Cal on AIN @ Selected Gain 3 × 1/Output Rate 4 × 1/Output Rate + t
P