ade7854 Analog Devices, Inc., ade7854 Datasheet - Page 36

• Manufacturer Part Number: ade7854
• Description: Poly Phase Multifunction Energy Metering Ic With Neutral Current Measurement
• Manufacturer: Analog Devices, Inc.

ADE7854
BWATTHR[31:0] and CWATTHR[31:0] represent the phase
Figure 46 explains this process. The WTHR[47:0] 48-bit signed
register contains the threshold. It is introduced by the user and
is common for both total and fundamental phase active powers.
Its value depends on how much energy is assigned to 1LSB of
watt-hour registers. Let’s suppose a derivative of wh [10
an integer, is desired as 1LSB of WATTHR. Then WTHR is
computed using the following expression:
where:
PMAX=33,516,139=0x1FF6A6B is the instantaneous power
computed when the ADC inputs are at full scale.
f
instantaneous power.
U
the ADC inputs are at full scale.
The maximum value that may be written on WTHR[47:0] is
2
write a number equal or greater than PMAX. Negative numbers
should never be used.
The WTHR[47:0] is a 48-bit register. As previously stated, the
serial ports of the ADE7854 work on 32, 16 or 8-bit words. As
presented in Figure 47, WTHR register is accessed as two 32-bit
WTHR
s
=8KHz is the frequency with which the DSP computes the
47
FS
accumulation in
v
-1. The minimum value is 0x0, but it is recommended to
A
active power
i
, I
A
generated
FS
pulses
DSP
DSP
are the rms values of phase voltages and currents when
=
APHCAL
PMAX
Figure 46. Active Power Accumulation inside DSP
U
WTHR[47:0]
⋅
f
FS
s
⋅
⋅
3600
I
FS
AVGAIN
AIGAIN
1 DSP pulse = 1LSB of WATTHR[47:0]
⋅
10
n
HPFDIS[23:0]
HPFDIS[23:0]
HPF
HPF
Integrator
Digital
Figure 45. ADE7854 Total Active Energy Accumulation
Digital Signal Processor
n
wh], n
(21)
LPF2
Rev. PrC| Page 36 of 71
AWATTOS
Σ
total active powers.
registers (WTHR1[31:0] and WTHR0[31:0]), each having 8
most significant bits padded with 0s.
This discrete time accumulation or summation is equivalent to
integration in continuous time following the description in
expression
where:
n is the discrete time sample number.
T is the sample period.
In the ADE7854, the total phase active powers are accumulated
in AWATTHR[31:0], BWATTHR[31:0] and CWATTHR[31:0]
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
would underflow to full-scale positive (0x7FFFFFFF) and
continue decreasing in value.
Bit 0 (AEHF) in STATUS0[31:0] register is set when bit 30 of
one of xWATTHR, x=A, B, C registers changes, signifying one
of these registers is half full. If the active power is positive, the
watt-hr register becomes half full when it increments from
0x3FFF FFFF to 0x4000 0000. If the active power is negative,
the watt-hr register becomes half full when it decrements from
0xC000 0000 to 0xBFFF FFFF.
Energy
31
0000 0000
AWGAIN
Figure 47. WTHR[47:0] is communicated as two 32-bit registers
=
∫
24
WTHR1[31:0]
(22
p
Σ
23
WTHR[47:0]
47
( )
t
).
24 bit signed number
dt
=
56 bits
Preliminary Technical Data
Lim
T
→
0
⎧
⎨
⎩
n
∑
∞
WTHR[47:0]
=
0
p
0
24
( )
nT
23
31
0000 0000
×
T
Σ
⎫
⎬
⎭
24
WTHR0[31:0]
23
STATUS0[31:0]
24 bit unsigned number
REVAPA bit in
AWATTHR[31:0]
32 bit register
0
(22)
0