MAXQ3180 Maxim, MAXQ3180 Datasheet - Page 59

• Manufacturer Part Number: MAXQ3180
• Description: The MAXQ3180 is a dedicated electricity measurement front-end that collects and calculates polyphase voltage, current, power, energy, and many other metering and power-quality parameters of a polyphase load
• Manufacturer: Maxim

negative (for a capacitive load). These values are sepa-
rately accumulated. This means that during any one
DSP cycle, only positive or negative reactive energy will
be accumulated.
Similarly, for real energy, the result accumulated during
any DSP cycle can be positive (that is, energy is deliv-
ered to the load) or negative (that is, energy is driven
back into the line). As is performed for reactive energy,
these values are separately accumulated.
Apparent energy is also accumulated, but since this
value is always positive or zero, there is only one
apparent energy accumulator.
From time to time, the accumulators generate an over-
flow. When this occurs, the appropriate bit is set in the
overflow status register X.EOVER.
When an overflow occurs, supervisory code running on
the host processor must make the appropriate adjust-
ments in the reported energy. In many cases, this could
simply involve incrementing an overflow counter. The
host processor must then clear the overflow indication.
The MAXQ3180 monitors the voltage signal on each
phase for zero-crossing events. If no ascending zero
crossings are detected within a specified number
(NZX_TIMO) of analog scan sample periods, the
NOZXF (X.FLAGS) flag is set by the MAXQ3180 to noti-
fy the master of this condition. If the NOZXM bit is set,
this flag sets the NOZX bit in the IRQ_FLAG. If the inter-
rupt enable bit ENOZX is set to 1, the interrupt signal
IRQ is driven low by the MAXQ3180 whenever NOZX =
Figure 12. Apparent and Reactive Energy Calculations
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________
No-Zero-Crossing Detection
E_RAW
E_RAW
REACTIVE
RAW_V
RAW_I
REAL
X × Y
X
X
2
2
+ Y
- Y
2
2
APPSEL
APPSEL
1. The master can clear NOZXF and NOZX back to 0 to
remove the interrupt condition.
A phase sequence status bit PHSEQ indicates the
order in which zero crossings are detected. When a
zero-crossing event occurs on the phase A voltage sig-
nal, followed by phase B, phase C, and then phase A
again, this bit cleared. If a zero crossing on phase A is
then followed by a zero crossing on phase C, then
phase B, this bit set to 1.
For each of the three phases, the MAXQ3180 calcu-
lates RMS voltage and RMS current values, as well as
determines active and reactive energy, using a line-
cycle-based integration process.
The power, energy, and RMS calculation process con-
sists of two tasks: continuous accumulation and post-
processing triggered every CYCNT line cycles. The
accumulation task accumulates raw data obtained from
the AFE during CYCNT line cycles. This task is per-
formed continuously in the background by the
MAXQ3180. When a CYCNT line cycles accumulation
stage has completed, which is determined by a dedi-
cated frame counter exceeding the NS level, the raw
integral accumulator values are saved for postprocess-
ing and cleared, beginning the next cycle of accumula-
tion task. Then, the DSP postprocessing is triggered to
RMS Voltage, RMS Current, and Energy
E_GAIN
E_GAIN
Power Calculation (Active, Reactive,
AVERAGE
AVERAGE
AVG_C
AVG_C
Phase Sequence Status
E
E
APPARENT
REACTIVE
Calculation
Apparent)
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