CS5463 datasheet(38/46 Pages) CIRRUS

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CS5463

DS678F3

each instantaneous measurement to nullify the DC

component present in the system during conversion

commands.

7.1.2.2 AC Offset Calibration Sequence

Corresponding offset registers IACoff and/or VACoff

should be cleared prior to initiating AC offset calibra-

tions. Initiate an AC offset calibration.The AC offset reg-

isters are updated with an offset value that reflects the

RMS output level. Upon completion of the AC offset cal-

ibration the AC offset is stored in the corresponding AC

offset register. The AC offset register value is subtract-

ed from each successive VRMS and IRMS calculation.

7.1.3 Gain Calibration Sequence

When performing gain calibrations, a reference signal

should be applied to the VIN

 pins of the voltage and

IIN

 pins of the current channels that represents the de-

sired maximum signal level. Figure 14 shows the basic

setup for gain calibration.

For gain calibrations, there is an absolute limit on the

RMS voltage levels that are selected for the gain cali-

bration input signals. The maximum value that the gain

registers can attain is 4. Therefore, if the signal level of

the applied input is low enough that it causes the

CS5463 to attempt to set either gain register higher than

4, the gain calibration result will be invalid and all

CS5463 results obtained while performing measure-

ments will be invalid.

If the channel gain registers are initially set to a gain oth-

er then 1.0, AC gain calibration should be used.

7.1.3.1 AC Gain Calibration Sequence

The corresponding gain register should be set to 1.0,

unless a different initial gain value is desired. Initiate an

AC gain calibration. The AC gain calibration algorithm

computes the RMS value of the reference signal applied

to the channel inputs. The RMS register value is then di-

vided into 0.6 and the quotient is stored in the corre-

sponding

gain

Each

instantaneous

measurement will be multiplied by its corresponding AC

gain value.

A typical rms calibration value which allows for reason-

able over-range margin would be 0.6 or 60% of the volt-

age and current channel’s maximum input voltage level.

Two examples of AC gain calibration and the updated

digital output codes of the channel’s instantaneous data

registers are shown in Figures 15 and 16. Figure 16

shows that a positive (or negative) DC-level signal can

be used even though an AC gain calibration is being ex-

ecuted.

External

Connections

IN +

IN -

XG AIN

Reference

Signal

Figure 14. System Calibration of Gain.

RMS Register =

230/ x

250 0.65054

250 mV

230 mV

0 V

-230 mV

-250 mV

0.9999...

0.92

-0.92

-1.0000...

RMS Register =0.600000

250 mV

230 mV

0 V

-230 mV

-250 mV

0.84853

-0.84853

Before AC Gain Calibration (Vgn Register = 1)

After AC Gain Calibration (Vgn Register changed to approx. 0.9223)

Instantaneous Voltage

Sinewave

0.92231

-0.92231

INPUT

SIGNAL

INPUT

SIGNAL

Figure 15. Example of AC Gain Calibration

RMS Register =

230 =

0.92

250 mV

230 mV

0 V

-250 mV

0.9999...

0.92

-1.0000...

RMS Register =0.600000

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 approx. 0.65217)

Instantaneous Voltage

DC Signal

0.65217

-0.65217

INPUT

SIGNAL

INPUT

SIGNAL

250

Figure 16. Example of AC Gain Calibration

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