ade7880 Analog Devices, Inc., ade7880 Datasheet - Page 44

• Manufacturer Part Number: ade7880
• Description: Polyphase Multifunction Energy Metering Ic With Harmonic Monitoring
• Manufacturer: Analog Devices, Inc.

ADE7880
Figure 50 explains this process. The threshold is formed by
concatenating the WTHR 8-bit unsigned register to 27 bits
equal to 0. It is introduced by the user and is common for total
active and fundamental powers on all phases. Its value depends
on how much energy is assigned to one LSB of watt-hour
registers. Supposing a derivative of wh [10
is desired as one LSB of the xWATTHR register, WTHR is
computed using the following expression:
where:
PMAX = 27,059,678=0x19CE5DE as the instantaneous power
computed when the ADC inputs are at full scale.
f
power computed by the DSP at 8KHz is accumulated.
U
the ADC inputs are at full scale.
WTHR register is an 8-bit unsigned number, so its maximum
value is 2
is 2 or 1 should be avoided and 0 should never be used as the
threshold must be a non-zero value.
This discrete time accumulation or summation is equivalent to
integration in continuous time following the description in
Equation 26.
where:
n is the discrete time sample number.
T is the sample period.
In the ADE7880, the total phase active powers are accumulated in
the AWATTHR, BWATTHR, and CWATTHR 32-bit signed
registers, and the fundamental phase active powers are
accumulated in AFWATTHR, BFWATTHR, and CFWATTHR
32-bit signed registers. The active energy register content can
roll over to full-scale negative (0x80000000) and continue
increasing in value when the active power is positive. Conversely, if
the active power is negative, the energy register underflows to
full-scale positive (0x7FFFFFFF) and continues decreasing in value.
S
FS
= 1.024MHz, the frequency at which every instantaneous
accumulation
, I
first stage of
active power
generated
after first
WTHR
FS
Energy
pulses
stage
are the rms values of phase voltages and currents when
8
Figure 50. Active Power Accumulation Inside the DSP
– 1. Its default value is 0x3. Values lower than 3, that
=
=
∫
PMAX
p
THRESHOLD
( )
t
U
dt
FS
×
=
×
f
Lim
S
T
1 pulse = 1LSB of WATTHR[31:0]
I
→
FS
×
0
3600



×
n
∑
∞
2
=
0
27
p
×
( )
10
nT
n
×
n
wh], n as an integer,
T



Rev. PrE | Page 44 of 103
(25)
(26)
The ADE7880 provides a status flag to signal when one of the
xWATTHR and xFWATTHR registers is half full. Bit 0 (AEHF)
in the STATUS0 register is set when Bit 30 of one of the
xWATTHR registers changes, signifying one of these registers is
half full. If the active power is positive, the watt-hour register
becomes half full when it increments from 0x3FFF FFFF to 0x4000
0000. If the active power is negative, the watt-hour register
becomes half full when it decrements from 0xC000 0000 to
0xBFFF FFFF. Similarly, Bit 1 (FAEHF) in STATUS0 register, is
set when Bit 30 of one of the xFWATTHR registers changes,
signifying one of these registers is half full.
Setting Bits[1:0] in the MASK0 register enable the FAEHF and
AEHF interrupts, respectively. If enabled, the IRQ0 pin is set
low and the status bit is set to 1 whenever one of the energy
registers, xWATTHR (for the AEHF interrupt) or xFWATTHR
(for the FAEHF interrupt), become half full. The status bit is
cleared and the
STATUS0 register with the corresponding bit set to 1.
Setting Bit 6 (RSTREAD) of the LCYCMODE register enables a
read-with-reset for all watt-hour accumulation registers, that is,
the registers are reset to 0 after a read operation.
Integration Time Under Steady Load
The discrete time sample period (T) for the accumulation register
is 976.5625ns (1.024MHz frequency). With full-scale sinusoidal
signals on the analog inputs and the watt gain registers set to
0x00000, the average word value from each LPF2 is PMAX
=27,059,678=0x19CE5DE. If the WTHR register threshold is
set at 3, its minimum recommended value, the first stage
accumulator generates a pulse that is added to watt-hour
registers every
The maximum value that can be stored in the watt-hour
accumulation register before it overflows is 2
0x7FFFFFFF. The integration time is calculated as
Energy Accumulation Modes
The active power is accumulated in each watt-hour
accumulation 32-bit register (AWATTHR, BWATTHR,
CWATTHR, AFWATTHR, BFWATTHR, and CFWATTHR)
according to the configuration of Bit 5 and Bit 4 (CONSEL bits) in
the ACCMODE register. The various configurations are
described in Table 14.
Table 14. Inputs to Watt-Hour Accumulation Registers
CONSEL
00
01
Time = 0x7FFF,FFFF × 14.531 μs = 8 hr 40 min 6 sec (27)
AWATTHR
VA × IA
VA × IA
PMAX
IRQ0 pin is set to logic high by writing to the
Preliminary Technical Data
3
×
×
. 1
2
024
27
×
BWATTHR
VB × IB
VB x IB
VB= VA − VC (See
Note)
10
6
=
14
.
531
µ
31
sec
− 1 or
.
CWATTHR
VC × IC
VC × IC