cs5467 Cirrus Logic, Inc., cs5467 Datasheet - Page 40

• Manufacturer Part Number: cs5467
• Description: Four-channel Power / Energy Ic
• Manufacturer: Cirrus Logic, Inc.

9. SYSTEM CALIBRATION
9.1 Calibration
The CS5467 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
The CS5467 must be operating in its active state and
ready to accept valid commands. Refer to
mands
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 + T
calibrations take at least 6( N ) + T
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 VIN1 ±
( VIN2 ±) or current inputs IIN1 ± (IIN2 ±) of the CS5467.
(see
40
Figure
In
on page 25.
11.)
Modulator
= READABLE/WRITABLE REGISTERS.
Filter
DC Offset
SETTLE
I1
I2
DCOFF
DCOFF
Negate
SETTLE
, V1
, V2
+
samples. AC offset
AC Gain
DCOFF
DCOFF
Figure 10. Calibration Data Flow
,
samples. As N
I1
I2
Figure
GAIN
GAIN
7.6 Com-
, V1
, V2
X
DC
1
GAIN
GAIN
AVG
DC Gain
10.
,
Σ
÷
V1, I1, V2, I2
N
N
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.
DC AVG
X
CM + -
0V + -
External
Connections
Figure 11. System Calibration of Offset
AIN+
AIN-
Σ
N
RMS
0.6
÷
N
+
-
√
AC Offset
XGAIN
I1
I2
ACOFF
ACOFF
+
Negate
, V1
, V2
+
+
ACOFF
ACOFF
RMS
,
I1
CS5467
I2
RMS
RMS
DS714F1
, V1
, V2
+
-
RMS
RMS
,