MAXQ3181-RAN+ datasheet(55/84 Pages) MAXIM

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Low-Power, Active Energy, Polyphase AFE

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Meter Pulse

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 MAXQ3181 supports one meter pulse output. This

output can be configured for either active positive 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 register, and then returns to

the inactive state (unless triggered again).

The PLS1_WD register contains the time in ADC frame

periods that the pulses remain in the active state when

triggered. By default, this register contains decimal 156

(0x9C) giving, at the default frame rate, a pulse width of

50ms.

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 energy

plus accumulated negative real energy). Other quanti-

ties include RMS voltage and current, positive and neg-

ative real energy. Select the desired accumulation

value in the QNSEL field of the PLSCFG1 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 register to include them in the accumulation.

Generating Pulses

On every DSP cycle, the MAXQ3181 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), then a pulse is started and the value in the

threshold register is subtracted from the value in the

pulse accumulator.

Meter Constant

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 register is

used to specify the meter constant according to the fol-

lowing formula:

In this formula, THR is the value to be written to the

threshold register, KM is the desired meter constant (in

pulses per kilowatt hour), IFS and VFS are the full-scale

voltage and current, respectively, and tFR is the frame

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

10-9 hours). The threshold register value can be calcu-

lated as:

65,536/(1600 x 102.4 x 0.5581 x 88.9 x 10-9) =

8,063,071 = 0x7B085F

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.)

Interrupts

The MAXQ3181 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 MAXQ3181 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:

PWRF: This flag indicates the VDVDD to the

MAXQ3181 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.

EOVF: Energy overflow. This flag indicates that one or

more energy accumulators (X.EAPOS, X.EANEG, etc.)

have overflowed. In a traditional meter, the host

processor would poll the MAXQ3181 to determine

which of the energy accumulators have overflowed and

adjust its internal accounting registers accordingly.

OC: The RMS current value on one or more of the

phases over the most recent DSP cycle has exceed-

ed the value set in the OCLVL register.

THR

MFS

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