Cirrus Logic CS5460A, Manual

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CS5460A
DS284PP4 37
bration sequence, we first define the various cali-
bration registers within the CS5460A.
4.8.2 The Calibration Registers
Refer to Figure 3 and Figure 25.
Voltage Channel DC Offset Register and Cur-
rent Channel DC Offset Register - Store additive
correction values that are used to correct for DC
offsets which may be present on the voltage/current
channels within the entire meter system. These
registers are updated by the CS5460A after a DC
offset calibration sequence has been executed.
Voltage Channel Gain Register and Current
Channel Gain Register - Store the multiplicative
correction values determined by the full-scale gain
calibration signals that are applied (by the user) to
the meter’s voltage/current channels. These regis-
ters are updated by the CS5460A after either an AC
or DC gain calibration sequence has been executed.
Voltage Channel AC Offset Register and Cur-
rent Channel AC Offset Register - Store additive
offset correction values that are used to correct for
AC offsets which may be created on the volt-
age/current channels within the entire meter sys-
tem. Although a noise signal may have an average
value of zero [no DC offset] the noise may still
have a non-zero rms value, which can add an unde-
sirable offset in the CS5460A’s Irms and Vrms re-
sults. These registers are updated by the CS5460A
after an AC offset calibration sequence has been
executed.
Referring to Figure 3, one should note that the AC
offset registers affect the output results differently
than the DC offset registers. The DC offset values
are applied to the voltage/current signals very early
in the signal path; the DC offset register value af-
fects all CS5460A results. This is not true for the
AC offset correction. The AC offset registers only
affect the results of the rms-voltage/rms-current
calculations.
Referring to Figure 3, the reader should note that
there are separate calibration registers for the AC
and DC offset corrections (for each channel). This
is not true for gain corrections, as there is only one
gain register per channel--AC and DC gain calibra-
tion results are stored in the same register. The re-
sults in the gain registers reflect either the AC or
DC gain calibration results, whichever was per-
formed most recently. Therefore, both a DC and
AC offset can be applied to a channel at the same
time, but only one gain calibration can be applied
to each channel. The user must decide which type
of gain calibration will be used: AC or DC, but not
both.
To summarize, for both the voltage channel and the
current channel, while the AC offset calibration se-
quence performs an entirely different function than
the DC offset calibration sequence, the AC gain
and DC gain calibration sequences perform the
same function (but they accomplish the function
using different techniques).
Since both the voltage and current channels have
separate offset and gain registers associated with
them, system offset or system gain can be per-
formed on either channel without the calibration
results from one channel affecting the other.
4.8.3 Calibration Sequence
1. The CS5460A must be operating in its active
state, and ready to accept valid commands via the
SPI interface, before a calibration sequence can be
executed. The user will probably also want to clear
the ‘DRDY’ bit in the Status Register.
2. The user should then apply appropriate calibra-
tion signal(s) to the “+” and “-” signals of the volt-
age/current channel input pairs. (The appropriate
calibration signals for each type of calibration se-
quence are discussed next, in Sections 4.8.4 and
4.8.5.)
3. Next the user should send the 8-bit calibration
command to the CS5460A serial interface. The