ADE7878ACPZ Analog Devices Inc, ADE7878ACPZ Datasheet - Page 37

• 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

REFERENCE CIRCUIT
The nominal reference voltage at the REF
0.075% V. This is the reference voltage used for the ADCs in the
ADE7878. The REF
source, for example, an external 1.2 V reference. The voltage of
the ADE7878 reference drifts slightly with temperature; see the
Specifications section for the temperature coefficient specification
(in ppm/°C). The value of the temperature drift varies from part
to part. Because the reference is used for all ADCs, any x% drift
in the reference results in a 2x% deviation of the meter accuracy.
The reference drift resulting from temperature changes is
usually very small and typically much smaller than the drift
of other components on a meter. Alternatively, the meter can
be calibrated at multiple temperatures.
If Bit 0 (EXTREFEN) in the CONFIG2[7:0] register is cleared to 0
(the default value), the ADE7878 uses the internal voltage refer-
ence. If the bit is set to 1, then the external voltage reference is used.
Set the CONFIG2 register during the PSM0 mode. Its value is
maintained during the PSM1, PSM2, and PSM3 power modes.
DIGITAL SIGNAL PROCESSOR
The ADE7878 contains a fixed function digital signal processor
(DSP) that computes all powers and rms values. It contains
various memories: program memory ROM, program memory
RAM, and data memory RAM.
The program used for the power and rms computations is
stored in the program memory ROM, and the processor executes
it every 8 kHz. The end of the computations is signaled by
setting Bit 17 (DREADY) to 1 in the STATUS0[31:0] register.
An interrupt attached to this flag can be enabled by setting
Bit 17 (DREADY) in the MASK0[31:0] register. If enabled, the
IRQ0 pin is set low and Status Bit DREADY is set to 1 at the end
of the computations. The status bit is cleared and the IRQ0 pin
is set to high by writing to the STATUS0[31:0] register with
Bit 17 (DREADY) set to 1.
The registers used by the DSP are located in the data memory
RAM at addresses between 0x4000 and 0x43FF. The width of
this memory is 28 bits.
As seen in the Power-Up Procedure section, at power-up or
after a hardware or software reset, the DSP is in idle mode. No
instruction is executed. All the registers located in the data
memory RAM are initialized at 0, their default values. The
Register Run[15:0] that is used to start and stop the DSP is
cleared to 0x0000. The Run[15:0] register must be written with
0x0001 for the DSP to start code execution. It is recommended
to first initialize all ADE7878 registers located in the data
memory RAM with their desired values and then write the
Run[15:0] register with 0x0001. In this way, the DSP starts the
computations from a desired configuration.
IN/OUT
pin can be overdriven by an external
IN/OUT
pin is 1.2 ±
Rev. 0 | Page 37 of 92
There is no obvious reason to stop the DSP if the ADE7878 is
maintained in PSM0 normal mode. All ADE7878 registers,
including ones located in the data memory RAM, can be
modified without stopping the DSP. However, to stop the DSP,
0x0000 must be written into Register Run[15:0]. To start the
DSP again, one of the following procedures must be followed:
•
•
As mentioned in the Power Management section, when the
ADE7878 switches out of PSM0 power mode, it is recommended
to stop the DSP by writing 0x0000 into the Run[15:0] register
(see Table 10 and Table 11 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 continuous
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 ADE7878 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, and is active in PSM0 and PSM1 modes. 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 53).
Then
If the ADE7878 registers located in the data memory RAM
have not been modified, write 0x0001 into Register Run[15:0]
to start the DSP.
If the ADE7878 registers located in the data memory RAM
have to be modified, first execute a software or a hardware
reset, initialize all ADE7878 registers at desired values, and
then write 0x0001 into Register Run[15:0] to start the DSP.
Frms
Frms
+
f
f
) (
2
2
t
) (
k
k
t
∑
,
≠
m
∞
=
m
=
=
=
=
2
1
∑
k
∞
=
∑
k
×
1
∞
=
F
1
1
t
F
N
1
k
F
k
∫
k
0
2
t
×
N
∑
N
f
2
=
−
F
2
1
sin
m
∑
k
( )
f
∞
t
=
2
1
sin
[ ]
dt
(
F
n
k
k
2
t ω
(
k
cos(
t ω
+
γ
+
2
k
k
γ
)
t ω
k
)
×
+
sin
γ
k
)
(
m
+
t ω
+
γ
m
)
ADE7878
(10)
(11)
(12)
(9)