MAXQ3181-RAN+ Maxim Integrated Products, MAXQ3181-RAN+ Datasheet - Page 63

• Manufacturer Part Number: MAXQ3181-RAN+
• Description: IC AFE POLYPHASE LO-PWR 28-TSSOP
• Manufacturer: Maxim Integrated Products

Specifications of MAXQ3181-RAN+

• Number Of Channels: 8
• Power (watts): 35mW
• Voltage - Supply, Analog: 3.3V
• Voltage - Supply, Digital: 3.3V
• Package / Case: 28-TSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Number Of Bits: -

The filter coefficient is a signed 16-bit value and can be
configured by master. Here Y denotes the global NS
value, X denotes individual NS measurements pro-
duced by zero-crossing events detected on the phase
A, B, or C voltage channel. Note that if all three phase
voltages present, the filter above receives three inputs
each DSP cycle. The global NS value is used to gener-
ate the trigger for DSP processing. Note that the NS
value can be configured by the master, which could be
necessary if all three voltage signals are lost and no
zero-crossings are detected. The line period is then
calculated as a product of NS and the scan frame t
The reciprocal of this value is the line frequency, which
can be obtained as a fixed-point value with 1 LSB =
0.001Hz by reading the LINEFR register.
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 MAXQ3181 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 MAXQ3181 to exit LOWPM
mode by reading the LOWPM_X bit (register address
0xC04).
The MAXQ3181 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 MAXQ3181
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
Low-Power Measurement Mode (LOWPM)
Low-Power, Active Energy, Polyphase AFE
______________________________________________________________________________________
Temperature
FR
.
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 MAXQ3181 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.
The current channel includes a variable-gain amplifier
that introduces a gain of 32 when the current falls
below the low current threshold (about 1/32 of full-scale
current I
FS
0x84F0 x 0.00911 - 273.15 = 36.8°C
(23 + 273.15)/0x7F00 = 0.00911K
). Because the gain of the amplifier cannot
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
Calibrating Linearity
i
hi
2 2
lo
and i
r
)
2
)
lo
hi
and r
) comfortably
lo
are the
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