MAXQ3180-RAN+ datasheet(59/101 Pages) MAXIM

59 / 101 page

Low-Power, Multifunction, Polyphase AFE

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AVERAGE

AVG_C

EAPPARENT

E_GAIN

APPSEL

X2 + Y2

E_RAWREAL

E_RAWREACTIVE

X2 - Y2

× Y

RAW_I

RAW_V

AVERAGE

AVG_C

EREACTIVE

E_GAIN

APPSEL

Figure 12. Apparent and Reactive Energy Calculations

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.

No-Zero-Crossing Detection

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 =

1. The master can clear NOZXF and NOZX back to 0 to

remove the interrupt condition.

Phase Sequence Status

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.

RMS Voltage, RMS Current, and Energy

Calculation

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.

Power Calculation (Active, Reactive,

Apparent)

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

MAXQ3180-RAN+ Datasheet(PDF) 59 Page - Maxim Integrated Products

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