MAXQ3180 Maxim, MAXQ3180 Datasheet - Page 62

• 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

Low-Power, Multifunction, Polyphase AFE
The purpose of a meter pulse is generally to advance a
mechanical counter when such a device is used as a
display. Meter pulses are also used during calibration
since time intervals can be measured with great preci-
sion.
The MAXQ3180 supports two meter pulse outputs.
These outputs can be configured for either active posi-
tive or active negative pulses by means of the POPOL
bit in the OPMODE1 register. When triggered, the pulse
goes to its active state and remains there for a period of
time defined by the PLS1_WD or PLS2_WD register,
and then returns to the inactive state (unless triggered
again).
The PLS1_WD and PLS2_WD registers contain the time
in ADC frame periods that the pulses remain in the
active state when triggered. By default, these registers
contain decimal 156 (0x9C) giving, at the default frame
rate, a pulse width of 50ms.
Each pulse generator can select one parameter to be
accumulated over any combination of the three phases.
For example, one could select real energy accumulated
over all three phases for pulse output 1, and reactive
energy accumulated over all three phases for pulse
output 2. The particular parameters that can be accu-
mulated are given in the register table.
Among the quantities that can be accumulated by the
pulse subsystem are the arithmetic active energy (that
is, the accumulated positive real energy minus the
accumulated negative real energy) and the absolute
active energy (that is, accumulated positive real ener-
gy plus accumulated negative real energy). Other
quantities include RMS voltage and current, positive
and negative real energy and reactive energy in each
of the four quadrants. Select the desired accumulation
value in the QNSEL field of the PLSCFG1 and
PLSCFG2 register.
Also in the pulse configuration registers you can select
which phases to include in the accumulation. Set any or
all the PHASEA, PHASEB, and PHASEC bits in the
PLSCFG1 or PLSCFG2 registers to include them in the
accumulation.
On every DSP cycle, the MAXQ3180 adds the value in
the selected register (or set of registers) to the pulse
accumulator. If the value in the pulse accumulator
exceeds the value in the associated threshold register
(THR1 or THR2), then a pulse is started and the value in
the threshold register is subtracted from the value in the
pulse accumulator.
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Generating Pulses
Meter Pulse
A meter constant is the number of pulses that are gen-
erated during a standard measurement interval; for
example, a meter might specify a meter constant of
1600 pulses per kilowatt-hour. The THR1 and THR2
registers are used to specify the meter constant
according to the following formula:
In this formula, THR is the value to be written to the
threshold register, K
pulses per kilowatt hour), I
voltage and current, respectively, and t
period in units of hours, as in the previous calculation.
As an example, assume once again a full-scale voltage
value of 558.1V = 0.5581kV, a full-scale current value of
102.4A, a desired meter constant of 1600 pulses per
kilowatt hour, and a default frame time of 320μs (88.9 x
10
lated as:
Increasing the value of the threshold register reduces
the meter constant (that is, there are fewer pulses per
kilowatt-hour); reducing the threshold register increases
the meter constant (that is, there are more pulses per
kilowatt-hour.)
The MAXQ3180 contains an interrupt subsystem to
relieve the host processor of the burden of constantly
polling the device for status. Instead, under certain cir-
cumstances, the MAXQ3180 can activate an external
pin to alert the host processor that some condition
requiring host attention has occurred.
Interrupts are managed globally by the IRQ_MASK and
IRQ_FLAG registers. In general, when a bit becomes
set in the IRQ_FLAG register, an interrupt is generated
if the corresponding bit is set in the IRQ_MASK register.
Interrupts can be configured for the following conditions:
-9
PWRF: This flag indicates the V
MAXQ3180 has fallen below its nominal operating
threshold (about 2.85V). This can be taken as an
indication that power failure is imminent and that the
host processor should begin taking steps to ensure
an orderly shutdown.
CHSCH: This flag indicates that the CHKSUM regis-
ter changed its value.
65,536/(1600 x 102.4 x 0.5581 x 88.9 x 10
hours). The threshold register value can be calcu-
THR
8,063,071 = 0x7B085F
=
M
K
M
is the desired meter constant (in
×
I
FS
FS
2
and V
×
16
V
FS
Meter Constant
FS
×
t
FR
are the full-scale
FR
DVDD
is the frame
Interrupts
-9
) =
to the