Maxim Integrated 78M6631 - Manual (Page 8)

78M6631 Firmware Description Document UG_6631_078
8 Rev 2
At the end of each accumulation interval, these measurements are provided to the MPU for post-
processing. Alternate multiplexer cycles also gather measurements of the IC’s junction temperature for
additional compensation in the MPU. Post-processing functions handled by the MPU at the end of every
accumulation interval include:
• Compensation for environmental variables
• Calculation of apparent power, power factor, phase angle, and line frequency
• Comparing of measurement outputs to configurable alarm thresholds
• Scaling and formatting of output measurement data
• Updating of all output registers (data and alarm status)
2.2.2 Front-End and Input Stage
Figure 3 shows the ADC signal path and signal processing for the voltage and current input channels.
SINC 3
DECIMATOR
IA
CROSS-
POINT
∆Σ
MODULATOR
PRECISION
REFERENCE
IA_RAW
VA_RAW
IB_RAW
VA1
F ADC
+250mv
ADC
X X
X X
VB_RAW
IA1
VA
IB
VB
IC
VC
IC_RAW
VC_RAW
IoffsA
VoffsA
Φ COMP
PCOMPA
TEMPERATURE
SENSOR
Temperature
Compensation
IgainA
+
VgainA
+
VB1
X X
X X
IB1
IoffsB
VoffsB
Φ COMP
PCOMPB
IgainB
+
VgainB
+
VC1
X X
X X
IC1
IoffsC
VoffsC
Φ COMP
IgainC
+
VgainC
+
PCOMPC
Φ COMP
Φ COMP
Φ COMP
Figure 3. Input Stage Signal Processing Path
The gray boxes are the gain calibration input registers. These registers can be modified by the user or by
the gain calibration routine for both voltage and current channels.
The voltage and current inputs channels are also temperature compensated. A compensation algorithm
based on the reading of an on-chip temperature sensor, corrects the gain in order to maintain the
accuracy across the temperature range.
The phase compensation block allows to digitally correct phase errors. These errors are usually
introduced by the voltage/current transformers or external filters. The phase error is calibrated by
introducing a time delay or a time advance, specified in the phase adjust registers.
The registers PCompA, PCompB, and PCompC can be modified by the user.
A configurable high-pass filter (HPF) in both voltage and current signal path removes any DC content
(offset) in the inputs.