CS5464 View Datasheet(PDF) - Cirrus Logic
Part Name
Description
MFG CO.
CS5464 Datasheet PDF : 46 Pages
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CS5464
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 (I2acoff) and/or
Vacoff (V2acoff) should be cleared prior to initiating AC
offset calibrations. Initiate an AC offset calibration.The
AC offset registers are updated with an offset value that
reflects the RMS output level. Upon completion of the
AC offset calibration the AC offset is stored in the corre-
sponding AC offset register. The AC offset register val-
ue is subtracted 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± (V2IN±) pins of the volt-
age and IIN± (I2IN±) pins of the current channels that
represents the desired maximum signal level. Figure 15
shows the basic setup for gain calibration.
External
Connections
+
+
Reference
IN+
Signal +-
XGAIN
-
-
CM +-
IN-
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 Figure 16 and 17. Figure 17
Before AC Gain Calibration (Vgn Register = 1)
250 mV
230 mV
Sinewave
INPUT 0 V
SIGNAL
0.9999...
0.92
Instantaneous Voltage
Register Values
-230 mV
-250 mV
-0.92
-1.0000...
VRMS Register = 230/√2 x 1/250 ≈ 0.65054
After AC Gain Calibration (Vgn Register changed to approx. 0.9223)
250 mV
Sinewave 230 mV
0.92231
0.84853
INPUT
SIGNAL 0 V
Instantaneous Voltage
Register Values
-230 mV
-250 mV
-0.84853
-0.92231
VRMS Register = 0.600000
Figure 16. Example of AC Gain Calibration
Figure 15. System Calibration of Gain.
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
CS5464 to attempt to set either gain register higher than
4, the gain calibration result will be invalid and all
CS5464 results obtained while performing measure-
ments will be invalid.
If the channel gain registers are initially set to a gain oth-
er than 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 register. Each instantaneous
Before AC Gain Calibration (Vgain Register = 1)
250 mV
230 mV
DC Signal
INPUT 0 V
SIGNAL
0.9999...
0.92
Instantaneous Voltage
Register Values
-250 mV
VRMS
Register
=
230
250
=
0.92
-1.0000...
After AC Gain Calibration (Vgain Register changed to approx. 0.65217)
250 mV
230 mV
DC Signal
INPUT 0 V
SIGNAL
0.65217
0.6000
Instantaneous Voltage
Register Values
-250 mV
-0.65217
VRMS Register = 0.600000
Figure 17. Example of AC Gain Calibration
40
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