CS5460A
DS284PP4
41
DC level is applied to the voltage channel inputs.
See Figure 23. The reader should compare Figure
22 to Figure 23 to see the difference between the
AC and DC calibration gain calibration sequences.
4.8.8 Duration of Calibration Sequence
The value of the Cycle Count Register (N) deter-
mines the number of conversions that will be per-
formed by the CS5460A during a given calibration
sequence. For DC offset/gain calibrations, the cal-
ibration sequence always takes at least N + 30 con-
version cycles to complete. For AC offset/gain
calibrations, the calibration sequence takes at least
6N + 30 A/D conversion cycles to complete, (about
6 computation cycles). If N is increased by the us-
er, the accuracy of calibration results will increase.
4.8.9
Is Calibration Required?
The CS5460A does not have to be calibrated. After
CS5460A is powered on and then reset, the device
is functional. This is called the active state. Upon
receiving
a
‘Start
Conversions’
command,
CS5460A can perform measurements without be-
ing calibrated. But the CS5460A’s output is always
affected by the values inside the various calibration
registers. If no calibrations are executed by the us-
er, then these registers will contain the default val-
ues (Gains = 1.0, DC Offsets = 0.0, AC Offsets =
0). Although the CS5460A can be used without
performing an offset or gain calibration, the guar-
V
RMS
Register =
230
/
250
x
1
/
√
2
≈
0.65054
250 mV
230 mV
0 V
-230 mV
-250 mV
0.9999...
0.92
-0.92
-1.0000...
V
RMS
Register =
0.6000...
250 mV
230 mV
0 V
-230 mV
-250 mV
0.84853
-0.84853
Before AC Gain Calibration (Vgain Register = 1)
After AC Gain Calibration (Vgain Register changed to ~0.9223)
Instantaneous Voltage
Register Values
Instantaneous Voltage
Register Values
Sinewave
Sinewave
0.92231
-0.92231
INPUT
SIGNAL
INPUT
SIGNAL
Figure 21. Example of AC Gain Calibration
V
RMS
Register =
230
/
250
=
0.92
250 mV
230 mV
0 V
-250 mV
0.9999...
0.92
-1.0000...
V
RMS
Register =
0.6000...
250 mV
230 mV
0 V
-250 mV
0.6000
Before AC Gain Calibration (Vgain Register = 1)
After AC Gain Calibration (Vgain Register changed to ~0.65217)
Instantaneous Voltage
Register Values
Instantaneous Voltage
Register Values
DC Signal
DC Signal
0.65217
-0.65217
INPUT
SIGNAL
INPUT
SIGNAL
Figure 22. Another Example of AC Gain Calibration
V
RMS
Register =
230
/
250
=
0.92
250 mV
230 mV
0 V
-250 mV
0.9999...
0.92
-1.0000...
V
RMS
Register =
0.9999...
230 mV
0 V
0.9999...
Before DC Gain Calibration (Vgain Register = 1)
After DC Gain Calibration (Vgain Register changed to 1.0870)
Instantaneous Voltage
Register Values
Instantaneous Voltage
Register Values
DC Signal
DC Signal
INPUT
SIGNAL
INPUT
SIGNAL
Figure 23. Example of DC Gain Calibration
Summary of Contents for CS5460A
Page 63: ... Notes ...
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