CS5460A
Note that when the calibration command is sent to
the CS5460A, the device must not be performing
A/D conversions (in either of the two acquisitions
modes). If the CS5460A is running A/D conver-
sions/computations in the ‘continuous computation
cycles’ acquisition mode (C = 1), the Pow-
er-Up/Halt Command must be issued first to termi-
3.8.6 Input Configurations for Calibrations
Figure 16 shows the basic setup for gain calibra-
tion. If a DC gain calibration is desired, a positive
DC voltage level must be applied, 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. To perform AC gain calibration instead of DC,
an AC reference signal should be applied that is
set to the desired maximum RMS level. Because
the voltage/current waveforms that must be mea-
sured in most power systems are approximately si-
nusoidal in nature, the RMS levels of the AC gain
calibration input signals may need to be set signif-
icantly lower than the voltage/current channel’s
maximum DC voltage input level. This must be
done in order to avoid the possibility that the peak
values of the AC waveforms that are to be mea-
sured will not register a value that would be outside
the available output code range of the voltage/cur-
rent A/D converters. For example, on the voltage
channel, if the Voltage Channel Gain Register is
set to it’s default power-on value of 1.000... before
calibration, then the largest pure sinusoidal wave-
form that can be used in AC calibration is one
whose RMS-value is ~0.7071 of the value of the
voltage channel’s peak DC input voltage value of
nate A/D conversions/computations.
If the
CS5460A is running A/D conversions/computa-
tions in the ‘single computation cycle’ data acquisi-
tion mode (C = 0), the Power-Up/Halt Command
must be issued first (unless the computation cycle
has completed) before executing any calibration
sequence. The calibration sequences will not run
if the CS5460A is running in either of the two avail-
able acquisition modes.
3.8.4 Calibration Signal Input Level
For both the voltage and current channels, the dif-
ferential voltage levels of the calibration signals
must be within the specified voltage input limits (re-
fer to “Differential Input Voltage Range” in Section
1., Characteristics and Specifications). For the
voltage channel the peak differential voltage level
can never be more than 500 mV . The same is
P-P
true for the current channel if the current channel
input PGA is set for 10x gain. If the the current
channel’s PGA gain is set to 50x, then the current
channel’s input limits are 100 mV
.
P-P
Note that for the AC/DC gain calibrations, there is
an absolute limit on the RMS/DC voltage levels (re-
spectively) that are selected for the voltage/current
channel gain calibration input signals. The maxi-
mum 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.
500 mV . Thus the maximum value of the input
P-P
sinusoid would be ~176.78 mV (rms). But in many
practical power metering situations, the RMS volt-
age input level of the AC gain calibration signal
may be reduced even further, to allow for some
over-ranging capability. A typical sinusoidal cali-
bration value which allows for reasonable
over-range margin would be 0.6 of the voltage/cur-
rent channel’s maximum input voltage level. For
the voltage channel, such a sine-wave would have
3.8.5 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 calibra-
tion signal will be at the same frequency as the fun-
damental power line frequency of the power
system that is to be metered.
a value of 0.6 x 250 mV
= 150 mV
.
rms
rms
For the offset calibrations, there is no difference
between the AC and DC calibration signals that
must be supplied: simply connect the “+” and “-’
29
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