MAXQ3180 Maxim, MAXQ3180 Datasheet - Page 71

• 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 order of the harmonic is set in ORDH field of the
AUX_CFG register.
Also in the AUX_CFG register are two bits that enable
the auxiliary channel and enable harmonic measure-
ment on the auxiliary channel. To enable the auxiliary
channel, set the ENAUX bit. Once set, the MAXQ3180
will perform an RMS calculation on the selected chan-
nel. This is useful only for the I
nel, since every other voltage and current already have
RMS calculations applied by default. (The DADCNV bit
should be cleared in the SCAN_IN register in order to
enable sampling the I
To enable harmonic measurement, set the ENHARM
bit. Now, the selected voltage or current signal is
passed to a filter that is identical to the second-order
fundamental filter, but that has separate parameters
(A1HARM, B0HARM).
This mode enables a subset of metering functions while
operating from the lower frequency internal RC oscilla-
tor to conserve power. The actual system clock fre-
quency used is the RC oscillator output frequency
divided by 8, which results in a system clock frequency
of approximately 1MHz.
The parameters provided in the LOWPM are:
• Voltage RMS
• Current RMS
• Ampere-Hour
The ampere-hour value is readable from the X.ESF reg-
isters (X = A/B/C). Entry to LOWPM mode only occurs
at the request of the master. The master must set the
LOWPM_E bit (register address 0xC03) to 1 to place
the MAXQ3180 into LOWPM mode. Entering LOWPM
mode changes the clock frequency, thereby invalidat-
ing a number of configuration registers. As a result, the
master must immediately reload the configuration regis-
ters and filter with new, updated values before metering
measurement operations can continue.
The master instructs the MAXQ3180 to exit LOWPM
mode by reading the LOWPM_X bit (register address
0xC04).
The MAXQ3180 contains a temperature sensor that can
be used by host software for any purpose, including
compensating power readings for temperature effects.
Use the virtual register command (RAWTEMP, 0xC01)
to perform a temperature conversion. The MAXQ3180
Low-Power Measurement Mode (LOWPM)
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________
N
channel.)
N
(neutral current) chan-
Temperature
returns raw ADC reading of voltage produced by the
temperature sensor.
Conversion from the arbitrary units to useful units (such
as degrees Celsius) requires taking one calibration
point and storing a conversion constant in the host
processor. The conversion constant is simply the value
(in absolute degrees) of one LSB.
To calculate the LSB value, take a reading at a known
temperature and divide the known temperature by the
reading. For example, assume you take a reading at
room temperature (23°C), and the reading is 0x7F00.
The degrees per LSB are then:
Now, assume at a later time you read the temperature
and see it is 0x84F0. To find the temperature in Celsius,
multiply by the degrees per LSB and subtract 273.15:
Ideal hardware should produce a current reading lin-
early proportional to the input current. However, due to
noise or other factors, the RMS current read by the
meter might not be precisely linear. The current offset
(X.OFFS_HI, X = A/B/C) can be used to compensate
the current channel nonlinearity.
Since the MAXQ3180 tracks the input current to deter-
mine what linearity compensation factors to use, the
user must choose two points (i
above the low current threshold, and get the X.IRMS
current readings (r
cept of the line drawn between the two points, that is,
the offset. To calculate the value for the offset register,
use the following formula. If LINFRM = 0:
In this equation, i
the current reading, respectively, in meter units at the
higher of the two reference currents; i
applied current and the current reading, respectively, in
meter units at the lower of the two reference currents.
The gain (X.I_GAIN) may require recalibration after the
offset register updated.
0x84F0 x 0.00911 - 273.15 = 36.8°C
(23 + 273.15)/0x7F00 = 0.00911K
offs
hi
lo
offs
and r
=
If LINFRM = 1:
and r
r
=
2
hi lo
24
hi
r i
2 2
2
hi
hi lo
Advanced Calibrations
i
4
). Then calculate the Y-inter-
are the applied current and
(
Calibrating Current Offset
i
(
hi
i
lo
−
−
2
−
i r
lo
i
−
hi lo
hi lo
i
i
hi
2 2
lo
and i
r
)
2
)
lo
hi
and r
) comfortably
lo
are the
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