ADE7878ACPZ Analog Devices Inc, ADE7878ACPZ Datasheet - Page 40

• 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
•
•
As mentioned in the Power Management section, when the
ADE7854/ADE7858/ADE7868/ADE7878 switch out of PSM0
power mode, it is recommended to stop the DSP by writing
0x0000 into the run register (see Table 11 and Table 12 for
the recommended actions when changing power modes).
ROOT MEAN SQUARE MEASUREMENT
Root mean square (rms) is a measurement of the magnitude of
an ac signal. Its definition can be both practical and mathematical.
Defined practically, the rms value assigned to an ac signal is the
amount of dc required to produce an equivalent amount of
power in the load. Mathematically, the rms value of a conti-
nuous signal f(t) is defined as
For time sampling signals, rms calculation involves squaring the
signal, taking the average, and obtaining the square root.
Equation 10 implies that for signals containing harmonics, the
rms calculation contains the contribution of all harmonics, not
only the fundamental. The ADE78xx uses two different methods
to calculate rms values. The first one is very accurate and is active
only in PSM0 mode. The second one is less accurate, uses the
estimation of the mean absolute value (mav) measurement, is
active in PSM0 and PSM1 modes, and is available for the
ADE7868 and ADE7878 only.
The first method is to low-pass filter the square of the input
signal (LPF) and take the square root of the result (see Figure 54).
Then
After the LPF and the execution of the square root, the rms
value of f(t) is obtained by
If the ADE7854/ADE7858/ADE7868/ADE7878 registers
located in the data memory RAM have not been modified,
write 0x0001 into the run register to start the DSP.
If the ADE7854/ADE7858/ADE7868/ADE7878 registers
located in the data memory RAM have to be modified, first
execute a software or a hardware reset, initialize all
ADE7854/ADE7858/ADE7868/ADE7878 registers at
desired values, enable the write protection, and then write
0x0001 into the run register to start the DSP.
F
F
+
F
f
f
) (
2
2
rms
rms
=
t
) (
k
k
t
∑
,
≠
m
∞
=
m
=
k
∑
=
∞
=
=
2
1
=
∑
k
∞
1
=
∑
k
×
1
F
∞
=
F
1
k
F
1
2
t
N
k
F
1
k
∫
k
2
0
×
t
N
∑
2
N
−
f
F
=
1
sin
2
m
∑
k
( )
f
∞
=
t
1
sin
2
(
F
[ ]
dt
k
n
k
2
t ω
(
k
cos(
t ω
+
γ
+
2
k
k
γ
)
t ω
k
)
×
+
sin
γ
k
)
(
m
+
t ω
+
γ
m
)
(10)
(11)
(12)
(13)
Rev. D | Page 40 of 96
(9)
The rms calculation based on this method is simultaneously
processed on all seven analog input channels. Each result is
available in the 24-bit registers: AIRMS, BIRMS, CIRMS,
AVRMS, BVRMS, CVRMS, and NIRMS (NIRMS is available
on the ADE7868 and ADE7878 only).
The second method computes the absolute value of the input
signal and then filters it to extract its dc component. It computes
the absolute mean value of the input. If the input signal in
Equation 12 has a fundamental component only, its average
value is
The calculation based on this method is simultaneously processed
only on the three phase currents. Each result is available in the
20-bit registers, which are available on the AE7868 and ADE7878
only: AIMAV, BMAV, and CMAV. Note that the proportionality
between mav and rms values is maintained for the fundamental
components only. If harmonics are present in the current channel,
the mean absolute value is no longer proportional to rms.
Current RMS Calculation
This section presents the first approach to compute the rms
values of all phase and neutral currents.
Figure 54 shows the detail of the signal processing chain for the
rms calculation on one of the phases of the current channel.
The current channel rms value is processed from the samples
used in the current channel. The current rms values are signed
24-bit values and they are stored into the AIRMS, BIRMS, CIRMS,
and NIRMS (ADE7868/ADE7878 only) registers. The update
rate of the current rms measurement is 8 kHz.
With the specified full-scale analog input signal of 0.5 V, the
ADC produces an output code that is approximately ±5,928,256.
The equivalent rms value of a full-scale sinusoidal signal is
4,191,910 (0x3FF6A6), independent of the line frequency. If
the integrator is enabled, that is, when Bit 0 (INTEN) in the
CONFIG register is set to 1, the equivalent rms value of a full-
scale sinusoidal signal at 50 Hz is 4,191,910 (0x3FF6A6) and at
60 Hz is 3,493,258 (0x354D8A).
The accuracy of the current rms is typically 0.1% error from
the full-scale input down to 1/1000 of the full-scale input when
PGA = 1. Additionally, this measurement has a bandwidth of
2 kHz. It is recommended to read the rms registers synchronous
to the voltage zero crossings to ensure stability. The IRQ1 inter-
rupt can be used to indicate when a zero crossing has occurred
(see the
the I rms measurement, which is the time it takes for the rms
register to reflect the value at the input to the current channel
when starting from 0.
F
F
DC
DC
Interrupts
=
=
T
1
π
2
⎡
⎢
⎢
⎢
⎣
×
T
2
∫
0
2
2
×
section).
×
F
F
1
1
×
sin(
t ω
Table 13
)
dt
−
T
T
∫
2
shows the settling time for
2
×
F
1
×
sin(
t ω
)
dt
⎤
⎥
⎥
⎥
⎦