CS5461 datasheet(19/45 Pages) CIRRUS

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CS5461

DS546F2

4.4.6.4 DC Gain Calibration Sequence

Based on the level of the positive DC calibration

voltage applied across the “+’ and “-” inputs, the

CS5461 determines the DC Gain Register value by

averaging the Instantaneous Register’s output sig-

nal values over one computation cycle (N samples)

and then dividing this average into 1. Therefore, af-

ter the DC gain calibration, the Instantaneous Reg-

ister will read at full-scale whenever the DC level

of the input signal is equal to the level of the DC

calibration signal applied to the inputs during the

DC gain calibration (see Figure 9).

4.4.7 Duration of Calibration Sequence

The value of the Cycle Count Register (N) deter-

mines the number of conversions performed by the

CS5461 during a given calibration sequence. For

DC offset/gain calibrations, the calibration se-

quence takes at least N + 30 conversion cycles to

complete. For AC offset/gain calibrations, the cali-

bration sequence takes at least 6N + 30 A/D con-

M odula to r

to V *, I*, P *, E * R e g is te rs

F ilte r

V RM S

SIN C

D C O ffse t*

Ga in *

-X

AC O ffset*

0.6

* Denotes readable/writable register

Figure 6. Calibration Data Flow

RMS Register =

230/

250 x

√2 ≈ 0.65054

250 mV

230 mV

0 V

-230 mV

-250 mV

0.9999...

0.92

-0.92

-1.0000...

RMS Register = 0.6000...

250 mV

230 mV

0 V

-230 mV

-250 mV

0.84853

-0.84853

Before AC Gain Calibration (Vgain Register = 1)

After AC Gain Calibration (Vgain Register changed to ~0.9223)

Instantaneous Voltage

Sinewave

0.92231

-0.92231

INPUT

SIGNAL

INPUT

SIGNAL

Figure 7. Example of AC Gain Calibration

RMS Register =

230/

250 = 0.92

250 mV

230 mV

0 V

-250 mV

0.9999...

0.92

-1.0000...

RMS Register = 0.6000...

250 mV

230 mV

0 V

-250 mV

0.6000

Before AC Gain Calibration (Vgain Register = 1)

After AC Gain Calibration (Vgain Register changed to ~0.65217)

Instantaneous Voltage

DC Signal

0.65217

-0.65217

INPUT

SIGNAL

INPUT

SIGNAL

Figure 8. Another Example of AC Gain Calibration

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