MAXQ3180 Maxim, MAXQ3180 Datasheet - Page 19

• 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

for system execution, a crystal warmup timer must
count 65,536 cycles of the high-frequency clock. While
this warmup time period is in effect, execution contin-
ues using the internal 1MHz oscillator. Once the
65,536-cycle count completes (which requires approxi-
mately 8.2ms at 8MHz), the device automatically
switches over to the high-frequency clock. This crystal
warmup timer is also activated upon exit from Stop
Mode, since the high-frequency crystal oscillator is shut
down during Stop Mode.
Instead of using a crystal oscillator to generate the
high-frequency clock, it is also possible to input a high-
frequency clock that has been generated by another
source (such as a digital oscillator IC) directly into the
XTAL1 pin of the MAXQ3180.
To use an external high-frequency clock as the system
clock source, the XTAL1 pin should be used as the
clock input and the XTAL2 pin should be left uncon-
nected. The master should also shut down the internal
crystal oscillator circuit by setting the EXTCLK bit
(OPMODE0.4) to 1. This bit is only cleared by the
MAXQ3180 if a power-on or brownout reset occurs and
is unaffected by other resets.
When using an external high-frequency clock, the clock
signal should be generated by a CMOS driver. If the
clock driver is a TTL gate, its output must be connected
to DVDD through a pullup resistor to ensure that the
correct logic levels are generated. To minimize system
noise in the clock circuitry, the external clock source
must meet the maximum rise and fall times and the
minimum high and low times specified for the clock
source in the Electrical Characteristics table.
When the external high-frequency crystal is warming
up, or when the MAXQ3180 is placed into LOWPM
mode, the system clock is sourced from an internal RC
oscillator. This internal oscillator is designed to provide
the system approximately 1MHz, although the exact
frequency varies over temperature and supply voltage.
If no external crystal circuit or high-frequency clock will
be used, the MAXQ3180 can be forced to operate infi-
nitely from the internal oscillator by grounding XTAL1.
This ensures that the crystal warmup count never com-
pletes, so the MAXQ3180 runs from the internal oscilla-
tor in all active modes.
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________
External High-Frequency Clock
Internal RC Oscillator
Before the MAXQ3180 can begin performing electric-
metering operations, the master must initialize a num-
ber of configuration parameters. Since the MAXQ3180
does not contain internal nonvolatile memory, these
parameters (stored in internal registers) must be set by
the master each time a power-up or reset cycle occurs,
or each time a switch is made between LOWPM Mode
and Run Mode.
The external master communicates with the MAXQ3180
over a standard SPI bus, using commands to read and
write values to internal registers on the MAXQ3180.
These registers include, among many other items:
• Operating mode settings (Stop Mode, LOWPM
• Status and interrupt flags (power-supply failure, over-
• Masking control for interrupts to determine which
• Configuration settings for analog channel scanning
• Power pulse output configuration
• Filter coefficients and configuration
• Read-only registers containing accumulated power
As the MAXQ3180 obtains voltage and current mea-
surements in Run Mode or LOWPM Mode, it accumu-
lates, filters, and performs a number of calculations on
the collected data. Many of these operations (including
the various filtering stages) are configured by settings
in registers written by the master. The output results
can then be read by the master from various read-only
registers in parallel with the ongoing measurement and
processing operations.
The SPI is an interdevice bus protocol that provides
fast, synchronous, full-duplex communications between
a designated master device and one or more slave
devices. In a MAXQ3180-based design, the
MAXQ3180 would be the slave device connected to a
designated master microcontroller.
The external master initiates all communications trans-
fers. The interrupt request line IRQ, while not technical-
ly part of the SPI bus interface, is also used for
master/slave communications because it allows the
MAXQ3180 to notify the master that an interrupt condi-
tion exists. Some SPI peripherals sacrifice speed in
favor of simulating a half-duplex operation. This is not
the case with the MAXQ3180; it is truly a full-duplex SPI
slave.
Mode, external clock mode, etc.)
current/overvoltage detection, etc.)
conditions cause IRQ to be driven low
and energy data
SPI Communications Rate and Format
Master Communications
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