ADE7878ACPZ Analog Devices Inc, ADE7878ACPZ Datasheet - Page 50

• Manufacturer Part Number: ADE7878ACPZ
• Description: IC ENERGY METERING 3PH 40LFCSP
• Manufacturer: Analog Devices Inc

Specifications of ADE7878ACPZ

• Input Impedance: 400 KOhm
• Measurement Error: 0.1%
• Voltage - I/o High: 2.4V
• Voltage - I/o Low: 0.4V
• Current - Supply: 22mA
• Voltage - Supply: 3 V ~ 3.6 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 40-WFQFN, CSP Exposed Pad
• Meter Type: 3 Phase
• Supply Voltage Range: 3V To 3.6V
• Operating Temperature Range: -40°C To +85°C
• Digital Ic Case Style: LFCSP
• No. Of Pins: 40
• Msl: MSL 1 - Unlimited
• Peak Reflow Compatible (260 C): Yes
• Supply Voltage Min: 3V
• Rohs Compliant: Yes
• Leaded Process Compatible: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

ADE7854/ADE7858/ADE7868/ADE7878
The average total reactive power over an integral number of line
cycles (n) is given by the expression in Equation 33.
where:
T is the period of the line cycle.
Q is referred to as the total reactive power. Note that the total
reactive power is equal to the dc component of the instantaneous
reactive power signal q(t) in Equation 32, that is,
This is the relationship used to calculate the total reactive power
in the ADE7858/ADE7868/ADE7878 for each phase. The
instantaneous reactive power signal, q(t), is generated by multi-
plying each harmonic of the voltage signals by the 90° phase-
shifted corresponding harmonic of the current in each phase.
The ADE7858/ADE7868/ADE7878 store the instantaneous
total phase reactive powers into the AVAR, BVAR, and CVAR
registers. Their expression is
where:
U
the ADC inputs are at full scale.
PMAX = 33,516,139, the instantaneous power computed when
the ADC inputs are at full scale and in phase.
The xVAR waveform registers can be accessed using various
serial ports. Refer to the Waveform Sampling Mode section for
more details.
The expression of fundamental reactive power is obtained from
Equation 33 with k = 1, as follows:
The ADE7878 computes the fundamental reactive power using
a proprietary algorithm that requires some initialization function
of the frequency of the network and its nominal voltage measured
in the voltage channel. These initializations are introduced in
the Active Power Calculation section and are common for both
fundamental active and reactive powers.
Table 17 presents the settling time for the fundamental reactive
power measurement, which is the time it takes the power to
reflect the value at the input of the ADE7878.
Table 17. Settling Time for Fundamental Reactive Power
63% Full Scale
375 ms
FS
, I
FQ = V
Q
Q
xVAR
FS
k
∑
∞
=1
are the rms values of the phase voltage and current when
=
=
V
nT
k
∑
∞
k
1
=
I
1
=
V
k
1
I
nT
∫
0
k
1
∑
k
sin(φ
∞
I
=
sin(φ
q
1
k
( )
U
U
t
sin(φ
FS
dt
k
k
1
– γ
×
– γ
=
k
I
I
∑
k
– γ
k
FS
∞
)
1
=
k
)
Input Signals
1
V
×
k
)
k
I
sin(φ
k
cos(φ
100% Full Scale
875 ms
k
– γ
k
– γ
k
) × PMAX ×
k
−
π
2
)
2
1
4
(33)
(34)
Rev. D | Page 50 of 96
Reactive Power Gain Calibration
The average reactive power from the LPF output in each phase can
be scaled by ±100% by writing to one of the phase’s VAR gain 24-bit
register (AVARGAIN, BVARGAIN, CVARGAIN, AFVARGAIN,
BFVARGAIN, or CFVARGAIN). The xVARGAIN registers are
placed in each phase of the total reactive power datapath. The
xFVARGAIN registers are placed in each phase of the fundamental
reactive power datapath. The xVARGAIN registers are twos com-
plement signed registers and have a resolution of 2
function of the xVARGAIN registers is expressed by
The output is scaled by –50% by writing 0xC00000 to the
xVARGAIN registers and increased by +50% by writing
0x400000 to them. These registers can be used to calibrate the
reactive power (or energy) gain in the ADE78xx for each phase.
As stated in the Current Waveform Gain Registers section, the
serial ports of the ADE7858/ADE7868/ADE7878 work on 32-,
16-, or 8-bit words and the DSP works on 28 bits. Similar to
registers presented in Figure 33, the AVARGAIN, BVARGAIN,
CVARGAIN, AFVARGAIN, BFVARGAIN, and CFVARGAIN
24-bit signed registers are accessed as 32-bit registers with the
four MSBs padded with 0s and sign extended to 28 bits.
Reactive Power Offset Calibration
The ADE7858/ADE7868/ADE7878 provide a reactive power
offset register on each phase and on each reactive power. AVAROS,
BVAROS, and CVAROS registers compensate the offsets in the
total reactive power calculations, whereas AFVAROS, BFVAROS,
and CFVAROS registers compensate offsets in the fundamental
reactive power calculations. These are signed twos complement,
24-bit registers that are used to remove offsets in the reactive
power calculations. An offset can exist in the power calculation
due to crosstalk between channels on the PCB or in the chip
itself. The offset resolution of the registers is the same as for the
active power offset registers (see the Active Power Offset
Calibration section).
As stated in the Current Waveform Gain Registers section, the
serial ports of the ADE7858/ADE7868/ADE7878 work on 32-,
16-, or 8-bit words and the DSP works on 28 bits. Similar to the
registers presented in Figure 33, the AVAROS, BVAROS, and
CVAROS 24-bit signed registers are accessed as 32-bit registers
with the four MSBs padded with 0s and sign extended to 28 bits.
Sign of Reactive Power Calculation
Note that the reactive power is a signed calculation. Table 18
summarizes the relationship between the phase difference between
the voltage and the current and the sign of the resulting reactive
power calculation.
Average
LPF
2
Output
Reactive
×
⎛
⎜
⎝
1
Power
+
xVARGAIN
=
2
23
Re
gister
⎞
⎟
⎠
−23
/LSB. The
(35)