MAXQ3181 Maxim, MAXQ3181 Datasheet - Page 13

• Manufacturer Part Number: MAXQ3181
• Description: The MAXQ3181 is a dedicated electricity measurement front-end that collects and calculates polyphase voltage, current, active power and energy, and many other metering parameters of a polyphase load
• Manufacturer: Maxim

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.
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.
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.
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
Low-Power, Active Energy, Polyphase AFE
______________________________________________________________________________________
Precision Pulse Generators
Detailed Description
Digital Signal Processor
Analog Front-End
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.
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.
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.
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
• Processes voltage and current samples through DSP
• Calculates power, energy, and other required quanti-
• Responds to register write and read commands from
• Outputs power pulse on CFP as configured.
• Drives IRQ when an interrupt condition has been
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.
voltage and current samples.
filters as enabled and configured.
ties and stores these values in RAM registers.
the master.
detected and the interrupt is not masked.
Operating Modes
SPI Peripheral
Stop Mode
Run Mode
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