ADE7880 Datasheet, PDF (38/104 Pages) Analog Devices – Polyphase Multifunction Energy Metering IC

ADE7880
Data Sheet
REFERENCE CIRCUIT
The nominal reference voltage at the REFIN/OUT pin is 1.2 ±
0.075% V. This is the reference voltage used for the ADCs in
the ADE7880. The REFIN/OUT pin can be overdriven by an
external source, for example, an external 1.2 V reference.
The voltage of the ADE7880 reference drifts slightly with
temperature; see the Specifications section for the temperature
coefficient specification (in ppm/°C). The value of the temperature
drift varies from part to part. Because the reference is used for
all ADCs, any x percentage drift in the reference results in a 2×
percentage deviation of the meter accuracy. The reference drift
resulting from temperature changes is usually very small and
typically much smaller than the drift of other components on a
meter. Alternatively, the meter can be calibrated at multiple
temperatures.
If Bit 0 (EXTREFEN) in the CONFIG2 register is cleared to 0 (the
default value), the ADE7880 uses the internal voltage reference.
If the bit is set to 1, the external voltage reference is used. Set the
CONFIG2 register during the PSM0 mode. Its value is maintained
during the PSM1, PSM2, and PSM3 power modes.
DIGITAL SIGNAL PROCESSOR
The ADE7880 contains a fixed function digital signal processor
(DSP) that computes all powers and rms values. It contains
program memory ROM and data memory RAM.
The program used for the power and rms computations is
stored in the program memory ROM and the processor executes
it every 8 kHz. The end of the computations is signaled by
setting Bit 17 (DREADY) to 1 in the STATUS0 register. An
interrupt attached to this flag can be enabled by setting Bit 17
(DREADY) in the MASK0 register. If enabled, the IRQ0 pin is
set low and Status Bit DREADY is set to 1 at the end of the
computations. The status bit is cleared and the IRQ0 pin is set
to high by writing to the STATUS0 register with Bit 17 (DREADY)
set to 1.
The registers used by the DSP are located in the data memory
RAM, at addresses between 0x4380 and 0x43BE. The width of
this memory is 28 bits. A two-stage pipeline is used when write
operations to the data memory RAM are executed. This means
two things: when only one register needs to be initialized, write
it two more times to ensure the value has been written into
RAM. When two or more registers need to be initialized, write
the last register in the queue two more times to ensure the value
has been written into RAM.
As explained in the Power-Up Procedure section, at power-up
or after a hardware or software reset, the DSP is in idle mode.
No instruction is executed. All the registers located in the data
memory RAM are initialized at 0, their default values and they
can be read/written without any restriction. The Run register,
used to start and stop the DSP, is cleared to 0x0000. The Run
register needs to be written with 0x0001 for the DSP to start
code execution. It is recommended to first initialize all ADE7880
registers located in the data memory RAM with their desired
values. Next, write the last register in the queue two additional
times to flush the pipeline and then write the Run register with
0x0001. In this way, the DSP starts the computations from a
desired configuration.
To protect the integrity of the data stored in the data memory
RAM of the DSP (between Address 0x4380 and Address
0x43BE), a write protection mechanism is available. By default,
the protection is disabled and registers placed between 0x4380
and 0x43BE can be written without restriction. When the
protection is enabled, no writes to these registers is allowed.
Registers can be always read, without restriction, independent
of the write protection state. To enable the protection, write
0xAD to an internal 8-bit register located at address 0xE7FE,
followed by a write of 0x80 to an internal 8-bit register located
at Address 0xE7E3. To disable the protection, write 0xAD to an
internal 8-bit register located at Address 0xE7FE, followed by a
write of 0x00 to an internal 8-bit register located at Address
0xE7E3. It is recommended to enable the write protection
before starting the DSP. If any data memory RAM based register
needs to be changed, simply disable the protection, change the
value and then enable back the protection. There is no need to
stop the DSP in order to change these registers.
The recommended procedure to initialize the registers located
in the data memory RAM is:
• Initialize all registers. Write the last register in the queue
three times to ensure its value was written into the RAM.
All the other registers of the ADE7880 should also be
initialized here.
• Enable the write protection by writing 0xAD to an internal
8-bit register located at Address 0xE7FE, followed by a write
of 0x80 to an internal 8-bit register located at Address 0xE7E3.
• Read back all data memory RAM registers to ensure they
were initialized with the desired values.
• In the remote case one or more registers are not initialized
correctly, disable the protection by writing 0xAD to an
internal 8-bit register located at Address 0xE7FE, followed
by a write of 0x00 to an internal 8-bit register located at
Address 0xE7E3. Initialize again the registers. Write the
last register in the queue three times. Enable the write
protection by writing 0xAD to an internal 8-bit register
located at Address 0xE7FE, followed by a write of 0x80 to
an internal 8-bit register located at Address 0xE7E3.
• Start the DSP by setting Run = 1.
There is no obvious reason to stop the DSP if the ADE7880 is
maintained in PSM0 normal mode. All ADE7880 registers,
including ones located in the data memory RAM, can be
modified without stopping the DSP. However, to stop the DSP,
0x0000 has to be written into Run register. To restart the DSP,
one of the following procedures must be followed:
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