MAXQ3180 Maxim, MAXQ3180 Datasheet - Page 61

• 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

The VOLT_CC and AMP_CC values can be calculated
from the full-scale voltage or full-scale current and the
desired value of one LSB in the display register:
Example: Assume the full-scale current is 102.4A, and
that we desire a 1nA LSB. The calculation would pro-
vide an AMP_CC value of:
The MAXQ3180 measures energy. But power is just
energy per unit time, and the MAXQ3180 keeps track of
the time unit over which energy is accumulated. This is
simply the NS value, the fractional number of samples
that comprises one DSP cycle. So converting energy to
power is as simple as dividing the accumulated energy
over one DSP cycle by NS. Multiplying by a conversion
constant (PWR_CC) gives power in user-established
units.
The power registers (PWRP.A, PWRP.B, PWRP.C,
PWRQ.A, PWRQ.B, PWRQ.C, PWRS.A, PWRS.B,
PWRS.C) are calculated by multiplying the accumulat-
ed energy (A.ACT, A.REA, A.APP, B.ACT, B.REA,
B.APP, C.ACT, C.REA, C.APP) by the conversion coeffi-
cient (PWR_CC) and then dividing by NS. The result is
the 48-bit average power over the most recent DSP
cycle, in units established by the conversion coefficient.
The PWR_CC value can be calculated from the full-
scale voltage, the full-scale current, and the desired
value of one LSB in the display register:
Example: For this example, assume the full-scale cur-
rent is 102.4A, the full-scale voltage is 558.1V, and that
the desired LSB is milliwatts after discarding the 16
LSB; that is, the desired LSB is 2
the following calculation:
Power factor is calculated as real power divided by
apparent power. But note that apparent power can be
calculated in either of two ways: either as a square root
of the sum of the squares of the real and reactive
power, or more commonly as the product of the RMS
102.4 x 558.1/(2
102.4/(2
VOLT CC
PWR CC
AMP CC
Low-Power, Multifunction, Polyphase AFE
24
______________________________________________________________________________________
_
_
_
32
x 10
x 2
=
=
=
-9
-16
2
2
2
) = 6104 = 0x17D8
32
24
24
x 10
I
FS
×
×
×
VOLT LSB
AMP LSB
PWR LSB
I
V
×
FS
-3
-16
FS
V
) = 872 = 0x0368
FS
_
_
milliwatts. Perform
_
Power Factor
Power
voltage and current measurement. The power factor as
reported could change when one or the other of these
methods is used.
The power factor is multiplied by 2
ed; thus, unity power factor is given by 16,384 decimal
(0x4000).
The line frequency is derived directly from the mean NS
values over the three phases. It is reported as millihertz;
thus, a 50Hz line frequency is reported as decimal
50,000 (0xC350).
The phasor angles are taken directly from the angular
measurement values determined at each DSP cycle.
The angle is reported in units of 0.01 degree; thus, a
120° phasor is reported as decimal 12,000 (0x2EE0).
Energy is read as the net energy directly scaled from
the appropriate registers. For example, the energy read
from the ENRP.A register (real energy, phase A) is
composed of the difference between the A.EAPOS (real
energy, positive direction, phase A) and A.EANEG (real
energy, negative direction, phase A) registers scaled
by the ENR_CC register.
Note that the energy registers (ENRP.A, ENRP.B,
ENRP.C, ENRP.T, ENRQ.A, ENRQ.B, ENRQ.C, ENRQ.T,
ENRS.A, ENRS.B, ENRS.C, ENRS.T) represent the ener-
gy, in every case, since the last overflow event. For this
reason, software must keep track of overflow and make
adjustments accordingly when using this register set.
To calculate the ENR_CC register value, begin with the
full-scale voltage and full-scale current, the frame time,
and the desired LSB value for energy. Then perform the
following calculation:
Example: It is essential to ensure that the correct units
are maintained throughout the calculation. In this exam-
ple, assume that the full-scale voltage is 558.1V, the
full-scale current is 102.4A, the frame time is the default
of 320μs, and the desired LSB is 100 milliwatt-hours
after the 32 bits are discarded; that is, the LSB is 0.1 x
2
given in microseconds and must be converted to hours
before the calculation can be performed: 320μs is 88.9
x 10
102.4 x 558.1 x 88.9 x 10
-32
-9
watt-hours. Notice, however, that the frame time is
hours. So the calculation proceeds as follows:
ENR CC
_
=
0x0D01
2
-9
I
FS
16
/(2
×
×
16
V
ENR LSB
FS
x 0.1 x 2
14
×
_
before it is report-
t
FR
Line Frequency
Phasor Angles
-32
) = 3329 =
Energy
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