ade7880 Analog Devices, Inc., ade7880 Datasheet - Page 41

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

Preliminary Technical Data
to full-scale ADC inputs, then multiplying them results in an
instantaneous power signal that has a dc component, V
Because LPF2 does not have an ideal brick wall frequency
response, the active power signal has some ripple due to the
instantaneous power signal. This ripple is sinusoidal and has a
frequency equal to twice the line frequency. Because the ripple
is sinusoidal in nature, it is removed when the active power
signal is integrated over time to calculate the energy. Bit 1
(LPFSEL) of CONFIG3 register selects the LPF2 strength. If
LPFSEL is 0 (default), the settling time is 650msec and the
ripple attenuation is 65dB. If LPFSEL is 1, the settling time is
1300msec and the ripple attenuation is 128dB. Figure 47 shows
the frequency response of LPF2 when LPFSEL is 0 and
VRMS x IRMS
0x19CE5DE =
= 54,119,356
0x339CBBC
27,059,678
0x000 0000
INSTANTANEOUS
i
POWER SIGNAL
v
) t (
) t (
=
=
2
Figure 46. Active Power Calculation
2
×
v
×
IRMS
i
A
VRMS
A
×
sin(
×
sin(
ω
) t
ω
APHCAL
p(t)=VRMS x IRMS - VRMS x IRMS x cos(2wt)
) t
AVGAIN
POWER SIGNAL: VRMS x IRMS
AIGAIN
INSTANTANEOUS ACTIVE
CONFIG3[0]
CONFIG3[0]
HPFEN bit
HPFEN bit
HPF
HPF
Figure 45. Total Active Power Data path
1
× I
Rev. PrE | Page 41 of 103
1
,
CONFIG[0]
INTEN bit
Digital Signal Processor
CONFIG3[1]
LPFSEL bit
and a sinusoidal component, V
the corresponding waveforms.
Figure 48 shows the frequency response of LPF2 when LPFSEL
is 1.
The ADE7880 stores the instantaneous total phase active
powers into the AWATT, BWATT, and CWATT registers. Their
expression is
where:
U
the ADC inputs are at full scale.
PMAX = 27,059,678 it is the instantaneous power computed
when the ADC inputs are at full scale and in phase.
The xWATT[23:0] waveform registers can be accessed using
various serial ports. Refer to the Waveform Sampling Mode
section for more details.
to Filter Instantaneous Power in Each Phase when LPFSEL bit of CONFIG3 is 0
FS
, I
xWATT
FS
–10
–15
–20
–25
are the rms values of the phase voltage and current when
–5
0
0.1
APGAIN
Figure 47. Frequency Response of the LPF Used
=
∑
k
∞
=
1
AWATTOS
U
U
FS
k
Σ
×
I
I
FREQUENCY (Hz)
FS
k
(default)
2
INSTANTANEOUS
PHASE A ACTIVE
:
×
4
1
cos(φ
× I
1
POWER
1
cos(2ωt); Figure 46 shows
k
AWATT
– γ
k
) × PMAX ×
3
ADE7880
2
1
10
4
(20)