Datasheet

Data Sheet ADE7880
Rev. A | Page 23 of 104
POWER-UP PROCEDURE
POR TIMER
TURNED ON
ADE7880
POWERED UP
ADE7880
ENTER PSM3
MICROPROCESSOR
SETS ADE7880
IN PSM0
MICROPROCESSOR
MAKES THE
CHOICE BETWEEN
I
2
C AND SPI
RSTDONE
INTERRUPT
TRIGGERED
40ms26ms
0V
3.3V – 10%
2.0V ± 10%
ADE7880
PSM0 READY
10193-009
Figure 34. Power-Up Procedure
The ADE7880 contains an on-chip power supply monitor that
supervises the power supply (VDD). At power-up, until VDD
reaches 2 V ± 10%, the chip is in an inactive state. As VDD
crosses this threshold, the power supply monitor keeps the chip
in this inactive state for an additional 26 ms, allowing VDD to
achieve 3.3 V − 10%, the minimum recommended supply
voltage. Because the PM0 and PM1 pins have internal pull-up
resistors and the external microprocessor keeps them high, the
ADE7880 always powers up in sleep mode (PSM3). Then, an
external circuit (that is, a microprocessor) sets the PM1 pin to a
low level, allowing the ADE7880 to enter normal mode (PSM0).
The passage from PSM3 mode, in which most of the internal
circuitry is turned off, to PSM0 mode, in which all functionality
is enabled, is accomplished in less than 40 ms (see Figure 34 for
details).
If PSM0 mode is the only desired power mode, the PM1 pin
may be set low permanently, using a direct connection to
ground. The PM0 pin may be left open because the internal pull
up resistor ensures its state is high. At power up, the ADE7880
briefly passes through PSM3 mode and then enters PSM0.
When the ADE7880 enters PSM0 mode, the I
2
C port is the
active serial port. If the SPI port is used, then the
SS
/HSA pin
must be toggled three times, high to low. This action selects the
SPI port for further use. If I
2
C is the active serial port, Bit 1
(I2C_LOCK) of the CONFIG2 register must be set to 1 to lock
it in. From this moment, the ignores spurious toggling
of the
ADE7880
SS
/HSA pin, and an eventual switch to use the SPI port is
no longer possible. Likewise, if SPI is the active serial port, any
write to the CONFIG2 register locks the port, at which time a
switch to use the I
2
C port is no longer possible. Only a power-
down or by setting the
RESET
pin low can the be
reset to use the I
2
C port. Once locked, the serial port choice is
maintained when the changes PSMx power modes.
ADE7880
ADE7880
Immediately after entering PSM0, the ADE7880 sets all registers
to their default values, including the CONFIG2 and LPOILVL
registers.
The ADE7880 signals the end of the transition period by triggering
the
IRQ1
interrupt pin low and setting Bit 15 (RSTDONE) in
the STATUS1 register to 1. This bit is 0 during the transition
period and becomes 1 when the transition ends. The status bit is
cleared and the
IRQ1
pin is returned high by writing the STATUS1
register with the corresponding bit set to 1. Because the RSTDONE
is an unmaskable interrupt, Bit 15 (RSTDONE) in the STATUS1
register must be cancelled for the
IRQ1
pin to return high. It is
recommended to wait until the
IRQ1
pin goes low before accessing
the STATUS1 register to test the state of the RSTDONE bit. At
this point, as a good programming practice, it is also recommended
to cancel all other status flags in the STATUS1 and STATUS0
registers by writing the corresponding bits with 1.
Initially, the DSP is in idle mode, which means it does not
execute any instruction. This is the moment to initialize all
ADE7880 registers. The last register in the queue must be
written three times to ensure the register has been initialized.
Then write 0x0001 into the Run register to start the DSP (see
the Digital Signal Processor section for details on the Run
register).
If the supply voltage, VDD, drops lower than 2 V ± 10%,
the ADE7880 enters an inactive state, which means that no
measurements or computations are executed.