CS5460A
38
DS284PP4
calibration command is an 8-bit command. Vari-
ous bits within this command specify the exact type
of calibration that is to be performed (e.g., AC gain
cal for voltage channel, DC offset cal for current
channel, etc.) The user must set or clear these bits
in the calibration command to correctly specify ex-
actly which calibration sequence is to be executed.
4. After the CS5460A has finished running the de-
sired internal calibration sequence and has stored
the updated calibration results in the appropriate
calibration registers, the DRDY bit is set (assuming
that it had previously been cleared) in the Status
Register to indicate that the calibration sequence
has been completed. If desired, the results of the
calibration can now be read from the appropriate
gain/offset registers, via the serial port.
Note that when the calibration command is sent to
the CS5460A by the user, the device must not be
performing A/D conversions (in either of the two
acquisitions modes). If the CS5460A is running
A/D conversions/computations in the ‘continuous
computation cycles’ acquisition mode (C=1), the
user must first issue the Power-Up/Halt Command
to terminate A/D conversions/computations. If the
CS5460A is running A/D conversions/computa-
tions in the ‘single computation cycle’ data acqui-
sition mode (C=0), then the user must either issue
the Power-Up/Halt Command, or else wait until the
computation cycle has completed, before executing
any calibration sequence. The calibration sequenc-
es will not run if the CS5460A is running in either
of the two available acquisition modes.
4.8.4 Calibration Signal Input Level
For both the voltage and current channels, the dif-
ferential voltage levels of the user-provided cali-
bration signals must be within the specified voltage
input limits (refer to “Differential Input Voltage
Range” in Section 1., Characteristics and Specifi-
cations). For the voltage channel the peak differen-
tial voltage level can never be more than
±
250 mV.
The same is true for the current channel if the cur-
rent channel input PGA is set for 10x gain. If the
user sets the current channel’s PGA gain to 50x,
then the current channel’s input limits are
±
50 mV.
Note that for the AC/DC gain calibrations, there is
an absolute limit on the RMS/DC voltage levels
(respectively) that are selected for the voltage/cur-
rent channel gain calibration input signals. The
maximum value that the gain register can attain is
4. Therefore, for either channel, if the voltage level
of a gain calibration input signal is low enough that
it causes the CS5460A to attempt to set either gain
register higher than 4, the gain calibration result
will be invalid, and after this occurs, all CS5460A
results obtained when the part is running A/D con-
versions will be invalid.
4.8.5 Calibration Signal Frequency
The frequency of the calibration signals must be
less than 1 kHz (assume MCLK/K = 4.096 MHz
and K = 1). Optimally, the frequency of the cali-
bration signal will be at the same frequency as the
fundamental power line frequency of the power
system that is to be metered.
4.8.6 Input Configurations for Calibrations
Figure 18 shows the basic setup for gain calibra-
tion. If a DC gain calibration is desired, the user
must apply a positive DC voltage level. The user
should set the value of this voltage such that it truly
represents the absolute maximum peak instanta-
neous voltage level that needs to be measured
across
the
inputs
(including
the
maximum
over-range level that must be accurately mea-
sured). In other words, the input signal must be a
positive DC voltage level that represents the de-
sired absolute peak full-scale value. However, in
many practical power metering situations, an AC
signal is preferred over a DC signal to calibrate the
gain. If the user decides to perform AC gain cali-
bration instead of DC, the user should apply an AC
reference signal that is set to the desired maximum
RMS level.
Because the voltage/current wave-
Summary of Contents for CS5460A
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