MAXQ3181-RAN+ datasheet(13/84 Pages) MAXIM

13 / 84 page

Low-Power, Active Energy, Polyphase AFE

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Detailed Description

The MAXQ3181 contains four major subsections: the

analog front-end, the digital signal processor, the preci-

sion pulse generators, and an SPI peripheral for com-

munication to the host processor.

Analog Front-End

The analog front-end (AFE) is an 8-channel analog-to-

digital converter (ADC). It operates autonomously in the

standard configuration, assigning three channels to

phase A, B, and C voltage; three channels to phase A,

B, and C current; one channel to neutral current; and

the last channel to a temperature sensor.

Each channel also contains a programmable-gain

amplifier capable of providing a gain of 1, 2, 4, 8, 16, or

32 incoming signals. Only the voltage channels permit

gain scaling by the host processor. The MAXQ3181

DSP firmware automatically sets the gain on current

channels.

Digital Signal Processor

The DSP code is permanently embedded in masked

ROM and accepts raw current and voltage samples for

each of three phases and continuously calculates a

host of values including RMS volts, RMS amps, real

energy, apparent energy, and power factor.

The MAXQ3181 DSP core processes incoming sam-

ples from the analog front-end according to user con-

figurations. The host sets these operating parameters

by specifying addresses within the device RAM space.

When a calculation cycle is complete, the results are

placed back into RAM as well. Thus, the DSP core uses

the RAM block as both its input (for operating parame-

ters) and output (for calculation results) medium. See

the

SPI Peripheral section for how the host writes oper-

ating parameters and reads results from the RAM.

The DSP also calculates certain values such as line fre-

quency and active power only when demanded by the

host.

Precision Pulse Generators

The MAXQ3181 includes a precision pulse generator

that generates a pulse whenever certain conditions are

met. In the MAXQ3181, many meter quantities can be

selected for conversion to meter pulses including

absolute energy, net energy, voltage, and current.

The pulse generator is an accumulator. On each DSP

cycle, whatever quantity is being measured—real ener-

gy, current, or something else—is added to the pulse

accumulator. The pulse accumulator is then tested to

determine if the value in the accumulator is greater than

the threshold. If it is greater, the threshold value is sub-

tracted from the accumulator value and the meter pulse

starts.

SPI Peripheral

The SPI controller is a slave-only device that can read

or write any location in the data RAM. Additionally, it

can request data from on-demand registers.

The MAXQ3181 implements a truly full-duplex commu-

nication, rather than the pseudo half-duplex mode used

by other SPI peripherals. That is, each time a character

is received by the MAXQ3181, a meaningful character

is returned to the host. Often, this is a protocol charac-

ter. In this way, the host can be assured that the com-

mand has been received and is valid. Optional error

checking can also be enabled to further guarantee

proper operation.

Operating Modes

The MAXQ3181 has two basic modes of operation,

each of which is described in the following sections.

The Initialization Mode is the default mode upon power-

up or following reset; entry to and exit from the other

operating modes is only performed as a result of com-

mands sent by the master.

Run Mode

This mode is the normal operating mode for the

MAXQ3181. In this mode, the MAXQ3181 continuously

executes the following operations:

• Scans analog front-end channels and collects raw

voltage and current samples.

• Processes voltage and current samples through DSP

filters as enabled and configured.

• Calculates power, energy, and other required quanti-

ties and stores these values in RAM registers.

• Responds to register write and read commands from

the master.

• Outputs power pulse on CFP as configured.

• Drives IRQ when an interrupt condition has been

detected and the interrupt is not masked.

Stop Mode

This mode places the MAXQ3181 into a power-saving

state where it consumes the least possible amount of

current. In Stop Mode, all functions are suspended,

including the ADC and power and voltage measurement

and processing. The MAXQ3181 does not respond to

any commands from the master in this operating state.

MAXQ3181-RAN+ Datasheet(PDF) 13 Page - Maxim Integrated Products

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