CS5461A-ISZ View Datasheet(PDF) - Cirrus Logic
Part Name
Description
MFG CO.
CS5461A-ISZ Datasheet PDF : 44 Pages
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CS5461A
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 11 shows the basic
setup for gain calibration.
External
Connections
+
+
Reference
Signal
+-
IN+
XGAIN
-
-
CM +-
IN-
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 12 and 13. Figure 13
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 12. Example of AC Gain Calibration
Figure 11. 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
CS5461A to attempt to set either gain register higher
than 4, the gain calibration result will be invalid and all
CS5461A 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 register. Each instantaneous
measurement will be multiplied by its corresponding AC
gain value.
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 13. Another Example of AC Gain Calibration
shows that a positive (or negative), DC-level signal can
be used even though an AC gain calibration is being ex-
36
DS661F2
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