CS5464-IS(2007) View Datasheet(PDF) - Cirrus Logic
Part Name
Description
MFG CO.
CS5464-IS Datasheet PDF : 46 Pages
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CS5464
9. SYSTEM CALIBRATION
9.1 Calibration
The CS5464 provides DC offset and gain calibration
that can be applied to the voltage and current measure-
ments, and AC offset calibration which can be applied to
the voltage and current RMS calculations.
Since the voltage and current channels have indepen-
dent offset and gain registers, offset and gain calibra-
tion can be performed on any channel independently.
The data flow of the calibration is shown in Figure 10.
The CS5464 must be operating in its active state and
ready to accept valid commands. Refer to 7.6 Com-
mands on page 24.
The value in the Cycle Count register (N) determines
the number of output word rate (OWR) samples that are
averaged during a calibration. DC offset and gain cali-
brations take at least N + TSETTLE samples. AC offset
calibrations take at least 6(N) + TSETTLE samples. As N
is increased, the accuracy of calibration results tends to
also increase.
The DRDY bit in the Status register will be set at the
completion of Calibration commands. If an overflow oc-
curs during calibration, other Status register bits may be
set as well.
9.1.1 Offset Calibration
During offset calibrations, no line voltage or current
should be applied to the meter. A zero-volt differential
signal can also be applied to the voltage inputs VIN± or
current inputs IIN1± (IIN2±) of the CS5464.
(see Figure 11.)
External
Connections
0V +-
AIN+
CM +-
AIN-
+
+
XGAIN
-
-
Figure 11. System Calibration of Offset
9.1.1.1 DC Offset Calibration
The DC Offset Calibration command measures and av-
erages DC values read on specified voltage or current
channels at zero input and stores the inverse result in
the associated offset registers. This will be added to in-
stantaneous measurements in subsequent conver-
sions, removing the offset.
Gain registers for channels being calibrated should be
set to 1.0 prior to performing DC offset calibration.
9.1.1.2 AC Offset Calibration
The AC Offset Calibration command measures the re-
sidual RMS values read on specified voltage or current
channels at zero input and stores the inverse result in
the associated AC offset registers. This will be added to
RMS measurements in subsequent conversions, re-
moving the offset.
AC offset registers for channels being calibrated should
first be cleared prior to performing the calibration.
V1, I1, V2, I2
In
Modulator
Filter
+
X
RMS
X
ΣN
÷N
√
+
+
+
I1RMS, V1RMS,
I2RMS, V2RMS
I1DCOFF, V1DCOFF, I1GAIN, V1GAIN,
I2DCOFF, V2DCOFF I2GAIN, V2GAIN
ΣN
DC Offset AC Gain
Negate
DC Gain
1
DCAVG
÷N
DC AVG
= READABLE/WRITABLE REGISTERS.
0.6
RMS
I1ACOFF, V1ACOFF,
I2ACOFF, V2ACOFF
AC Offset
Negate
Figure 10. Calibration Data Flow
DS682F1
39
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