cs5461 Cirrus Logic, Inc., cs5461 Datasheet - Page 19

• Manufacturer Part Number: cs5461
• Description: Single-phase, Bidirectional Power/energy Ic
• Manufacturer: Cirrus Logic, Inc.

4.4.6.4 DC Gain Calibration Sequence
Based on the level of the positive DC calibration
voltage applied across the “+’ and “-” inputs, the
CS5461 determines the DC Gain Register value by
averaging the Instantaneous Register’s output sig-
nal values over one computation cycle (N samples)
and then dividing this average into 1. Therefore, af-
ter the DC gain calibration, the Instantaneous Reg-
ister will read at full-scale whenever the DC level
of the input signal is equal to the level of the DC
DS546F2
In
Sinewave
Sinewave
SIGNAL
SIGNAL
INPUT
INPUT
Figure 7. Example of AC Gain Calibration
-230 mV
-250 mV
-230 mV
-250 mV
250 mV
230 mV
250 mV
230 mV
After AC Gain Calibration (Vgain Register changed to ~0.9223)
Before AC Gain Calibration (Vgain Register = 1)
M odulator
0 V
0 V
V
RMS
V
RMS
Register =
Register = 0.6000...
Filter
230
/
250
x
1
/
* Denotes readable/writable register
D C O ffse t*
√2
≈ 0.65054
-X
+
+
+
-0.84853
-0.92231
-1.0000...
-0.92
0.92231
0.84853
0.9999...
0.92
Figure 6. Calibration Data Flow
Instantaneous Voltage
Instantaneous Voltage
Register Values
Register Values
G a in *
x
1
x
Σ
÷
N
N
to V *, I*, P *, E * R egisters
X
2
calibration signal applied to the inputs during the
DC gain calibration (see Figure 9).
4.4.7 Duration of Calibration Sequence
The value of the Cycle Count Register (N) deter-
mines the number of conversions performed by the
CS5461 during a given calibration sequence. For
DC offset/gain calibrations, the calibration se-
quence takes at least N + 30 conversion cycles to
complete. For AC offset/gain calibrations, the cali-
bration sequence takes at least 6N + 30 A/D con-
A C O ffse t*
Figure 8. Another Example of AC Gain Calibration
+
DC Signal
DC Signal
SIGNAL
SIGNAL
+
INPUT
INPUT
-
-250 mV
-250 mV
250 mV
230 mV
Before AC Gain Calibration (Vgain Register = 1)
250 mV
230 mV
After AC Gain Calibration (Vgain Register changed to ~0.65217)
S IN C
0 V
0 V
2
X
0 .6
x
V
2
RMS
V
N
RMS
Register =
Register = 0.6000...
X
230
/
250
÷
= 0.92
N
-0.65217
CS5461
-1.0000...
0.65217
0.9999...
0.92
0.6000
Instantaneous Voltage
Instantaneous Voltage
Register Values
Register Values
V R M S
*
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