Cirrus Logic AN365 - Manual (Page 4)

AN365
4 AN365REV1
3.2 PGA Selection on the Current Channel
The CS5480 current channel incorporates a programmable gain amplifier (PGA) with two selectable input gains.
The Config0 register bits I1PGA[1:0] select either 10x or 50x gain for the current channel. The two PGA settings
dictate the maximum input voltage that can be applied to the IIN± inputs.
The Rogowski coil output voltage produced with the maximum AC line current (I
max
) should not exceed the max-
imum input voltages listed in Table 2. Some margin should be considered according design requirements.
3.3 Filter Selection
The CS5480 high-pass filter (HPF) and integrator are set using the Config2 register. To support a Rogowski coil,
HPF must be enabled on the voltage channel and the integrator must be enabled on the current channel.
3.4 Calibration and Compensation
To compensate for the tolerances and variations in components and to remove the residual offset and noise in
the system, a gain calibration, phase compensation, AC offset calibration, and power offset correction should
be performed. For more information, see the CS5480 data sheet, entitled Three Channel Energy Measurement
IC, for details regarding the calibration and compensations process.
4. Measurement Accuracy Results with Rogowski Coils
The CS5480 load performance (measurement accuracy under different load conditions) has been tested with three
different types of Rogowski coil. The active and reactive energy load performance is tested with a single energy
pulse. The meter constant is set at 2000 impulses per kWh, or 2000 impulses per kVarh. The I
RMS
load performance
is calculated based on CS5480 I
RMS
register values. All of the tests were conducted at room temperature and with
U
n
= 240V and line frequency of 50Hz.
CS5480 I-channel PGA Maximum Input Voltage
10x 167mV
RMS
50x 35mV
RMS
Table 2. PGA Settings