AD7715_15 datasheet(18/40 Pages) AD

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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, tP, to correctly scale the results of this first

conversion. tP will never exceed 2000 × tCLK 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 + tP

Internal FS Cal @ Selected Gain

ZS System Calibration

1, 0

ZS Cal on AIN @ Selected Gain

3 × 1/Output Rate

4 × 1/Output Rate + tP

FS System Calibration

1, 1

FS Cal on AIN @ Selected Gain

3 × 1/Output Rate

4 × 1/Output Rate + tP

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