AD7731

–21–

REV. 0

CALIBRATION OPERATION SUMMARY

The AD7731 contains a number of calibration options as outlined previously. Table XVI summarizes the calibration types, the op-

erations involved and the duration of the operations. There are two methods of determining the end of calibration. The first is to

monitor the hardware

RDY pin using either interrupt-driven or polling routines. The second method is to do a software poll of the

RDY bit in the Status Register. This can be achieved by setting up the part for continuous reads of the Status Register once a calibra-

tion has been initiated. The

RDY pin and RDY bit go high on initiating a calibration and return low at the end of the calibration

routine. At this time, the MD2, MD1, MD0 bits of the Mode Register have returned to 0, 0, 0. The FAST and SKIP bits are treated

as 0 for the calibration sequence so the full filter is always used for the calibration routines. See Calibration section for full details.

Table XVI. Calibration Operations

MD2, MD1, Duration to

RDY Duration to RDY

Calibration Type

MD0

Low (CHP = 1)

Low (CHP = 0)

Calibration Sequence

Internal Zero-Scale

1, 0, 0

22

× 1/Output Rate 24 × 1/Output Rate Calibration on internal shorted input with PGA set

for selected input range. The Offset Calibration

Register for the selected channel is updated at the

end of this calibration sequence. For full self-cali-

bration, this calibration should be preceded by an

Internal Full-Scale calibration. For applications

which require an Internal Zero-Scale and System

Full Scale calibration, this Internal Zero-Scale

calibration should be performed first.

Internal Full-Scale

1, 0, 1

44

× 1/Output Rate 48 × 1/Output Rate Calibration on internally-generated input full-scale

with PGA set for selected input range. The Gain

Calibration Register for the selected channel is

updated at the end of this calibration sequence. It is

recommended that internal full-scale calibrations

are performed on the operating input range except

for the 20 mV and 40 mV input ranges where opti-

mum results are achieved by calibrating on the

80 mV range. This calibration should be followed

by either an Internal Zero-Scale or System Zero-

Scale calibration. This calibration should be fol-

lowed by either an Internal Zero-Scale or System

Zero-Scale calibration. This zero-scale calibration

should be performed at the operating input range.

System Zero-Scale

1, 1, 0

22

× 1/Output Rate 24 × 1/Output Rate Calibration on externally-applied input voltage with

PGA set for selected input range. The input applied

is assumed to be the zero-scale of the system. For

full system calibration, this System Zero-Scale

calibration should be performed first. For applica-

tions which require a System Zero-Scale and Inter-

nal Full Scale calibration, this calibration should be

preceded by the Internal Full-Scale calibration. The

Offset Calibration Register for the selected channel

is updated at the end of this calibration sequence.

System Full-Scale

1, 1, 1

22

× 1/Output Rate 24 × 1/Output Rate Calibration on externally-applied input voltage with

PGA set for selected input range. The input applied

is assumed to be the full-scale of the system. This

calibration should be preceded by a System Zero-

Scale or Internal Zero-Scale calibration. The Gain

Calibration Register for the selected channel is

updated at the end of this calibration sequence.