ADA4255ACPZ-R7 datasheet(33/64 Pages) AD

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Data Sheet

ADA4255

THEORY OF OPERATION

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Rev. 0 | 33 of 64

Table 7. Gain Calibration Register Contents1

Name

G[3:0]

Contents

0x25

GAIN_CAL22

0b011x

Additional gain error for G = 4 V/V × 1.25 V/V or G = 8 V/V × 1.25 V/V

0x26

GAIN_CAL23

0b100x

Additional gain error for G = 16 V/V × 1.25 V/V or G = 32 V/V × 1.25 V/V

0x27

GAIN_CAL24

0b101x

Additional gain error for G = 64 V/V × 1.25 V/V or G = 128 V/V × 1.25 V/V

1 X means don’t care.

For all gains using 1 V/V scalar, calculate the gain error using the

following equation:

Gain Error = ((−1) × GAIN_CALx, Bit 4 + (100) × GAIN_CALx,

Bits[3:0]) (ppm)

For all gain values using 1.375 V/V or 1.25 V/V scalars, an addition-

al gain error (GE’) must be added, using this equation:

GE’ = Gain Error + ((−1) × GAIN_CALx, Bit 4 + (50) × GAIN_CALx,

Bits[3:0]) (ppm)

For example, assume that the ADA4255 is set to a gain of 32 V/V

and a scaling gain of 1.375 V/V. To calculate the stored gain

error, read the gain error stored in the GAIN_CAL10 register and

calculate the error in ppm. In this example, assume this readback is

10101, corresponding to a gain error of −500 ppm.

Then, read the additional gain error stored in GAIN_CAL17 and

calculate the error in ppm. In this example, assume this readback is

00010, corresponding to an additional gain error of 100 ppm. The

two errors are added to give a total gain error of −400 ppm.

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