ADE7758ARW Analog Devices Inc, ADE7758ARW Datasheet - Page 37

• Manufacturer Part Number: ADE7758ARW
• Description: IC ENERGY METERING 24-SOIC
• Manufacturer: Analog Devices Inc

Specifications of ADE7758ARW

• Rohs Status: RoHS non-compliant
• Input Impedance: 380 KOhm
• Measurement Error: 0.1%
• Voltage - I/o High: 2.4V
• Voltage - I/o Low: 0.8V
• Current - Supply: 8mA
• Voltage - Supply: 4.75 V ~ 5.25 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-SOIC (0.300", 7.50mm Width)
• Meter Type: 3 Phase
• Lead Free Status / RoHS Status: Not Compliant

Reactive Energy Calculation
Reactive energy is defined as the integral of reactive power.
Similar to active power, the ADE7758 achieves the integration
of the reactive power signal by continuously accumulating the
reactive power signal in the internal 41-bit accumulation
registers. The VAR-hr registers (AVARHR, BVARHR, and
CVARHR) represent the upper 16 bits of these internal
registers. This discrete time accumulation or summation is
equivalent to integration in continuous time. Equation 35
expresses the relationship
where:
n is the discrete time sample number.
T is the sample period.
Figure 72 shows the signal path of the reactive energy accumula-
tion. The average reactive power signal is continuously added
to the internal reactive energy register. This addition is a signed
operation. Negative energy is subtracted from the reactive energy
register. The average reactive power is divided by the content
of the VAR divider register before it is added to the corresponding
VAR-hr accumulation registers. When the value in the
VARDIV[7:0] register is 0 or 1, the reactive power is accumulated
without any division.
Reactive
Reactive
V
I
Energy
0xD7AE14
Energy
0x2851EC
0xD7AE
0x2852
CURRENT SIGNAL–i(t)
VOLTAGE SIGNAL–v(t)
0x00
0x00
=
PHCAL[6:0]
=
HPF
∫
∫
q
q
Φ
( )
( )
t
t
dt
SHIFTING FILTER
dt
=
90° PHASE
Lim
T
→
π
2
0
⎧
⎨
⎩
n
∑
∞
=
0
q
MULTIPLIER
( )
nT
×
Figure 72. ADE7758 Reactive Energy Accumulation
T
SIGN 2
⎫
⎬
⎭
LPF2
6
VAROS[11:0]
(34)
(35)
Rev. D | Page 37 of 72
+
2
0
+
2
VARG[11:0]
–1
2
–2
VARDIV[7:0]
2
VARDIV is an 8-bit unsigned register that is useful to lengthen
the time it takes before the VAR-hr accumulation registers
overflow.
Similar to reactive power, the fastest integration time occurs
when the VAR gain registers are set to maximum full scale,
that is, 0x7FF. The time it takes before overflow can be scaled
by writing to the VARDIV register; and, therefore, it can be
increased by a maximum factor of 255.
When overflow occurs, the VAR-hr accumulation registers
content can rollover to full-scale negative (0x8000) and continue
increasing in value when the reactive power is positive. Con-
versely, if the reactive power is negative, the VAR-hr accumulation
registers content can roll over to full-scale positive (0x7FFF)
and continue decreasing in value.
By setting the REHF bit (Bit 1) of the interrupt mask register,
the ADE7758 can be configured to issue an interrupt ( IRQ )
when Bit 14 of any one of the three VAR-hr accumulation
registers has changed, indicating that the accumulation register
is half full (positive or negative).
Setting the RSTREAD bit (Bit 6) of the LCYMODE register
enables a read-with-reset for the VAR-hr accumulation
registers; that is, the registers are reset to 0 after a read
operation.
–3
%
2
–4
+
+
40
15
VARHR[15:0]
TOTAL REACTIVE POWER IS
ACCUMULATED (INTEGRATED) IN
THE VAR-HR ACCUMULATION REGISTERS
0
0
ADE7758