Cirrus Logic CS5526 - Manual (Page 18)

CS5525 CS5526
18 DS202F5
VREF- as shown in Figure 12. For any input range
other than the 2.5 V range, the modulator gain error
can not be completely calibrated out. This is due to
the lack of an accurate full scale voltage internal to
the chips. The 2.5 V range is an exception because
the external reference voltage is 2.5 V nominal and
is used as the full scale voltage. In addition, when
self-calibration of gain is performed in the 25 mV,
55 mV, and 100 mV input ranges, the instrumenta-
tion amplifier’s gain is not calibrated. These two
factors can leave the converters with a gain error of
up to ±20% after self-calibration of gain. There-
fore, a system gain is required to get better accura-
cy, except for the 2.5 V range.
System Calibration
For the system calibration functions, the user must
supply the converters calibration signals which rep-
resent ground and full scale. When a system offset
calibration is performed, a ground reference signal
must be applied to the converter. See Figures 13
and 14. As shown in Figures 15 and 16, the user
must input a signal representing the positive full
scale point to perform a system gain calibration. In
either case, the calibration signals must be within
the specified calibration limits for each specific
calibration step (refer to the System Calibration
Specifications).
AIN+
AIN-
OPEN
+
-
X20
+
-
OPEN
CLOSED
VREF+
CLOSED
VREF-
+
-
Reference
Figure 12. Self Calibration of Gain (All Ranges).
+
-
X20
+
-
External
Connections
0V +
-
AIN+
AIN-
CM + -
Figure 13. System Calibration of Offset (Low Ranges).
+
-
X20
+
-
External
Connections
+
-
AIN+
AIN-
CM + -
0V
Figure 14. System Calibration of Offset (High Ranges).
+
-
X20
+
-
External
Connections
Full S cale +-
AIN+
A IN-
CM
+
-
Figure 15. System Calibration of Gain (Low Ranges)
+
-
X20
+
-
External
Connections
Full Scale +
-
AIN+
AIN-
CM +
-
Figure 16. System Calibration of Gain (High Ranges).