ADE7758ARW Analog Devices Inc, ADE7758ARW Datasheet - Page 32

• 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

ADE7758
The ADE7758 achieves the integration of the active power
signal by continuously accumulating the active power signal in
the internal 41-bit energy registers. The watt-hr registers
(AWATTHR, BWATTHR, and CWATTHR) represent the upper
16 bits of these internal registers. This discrete time
accumulation or summation is equivalent to integration in
continuous time. Equation 20 expresses the relationship.
where:
n is the discrete time sample number.
T is the sample period.
Figure 66 shows a signal path of this energy accumulation. The
average active power signal is continuously added to the internal
active energy register. This addition is a signed operation.
Negative energy is subtracted from the active energy register.
Note the values shown in Figure 66 are the nominal full-scale
values, that is, the voltage and current inputs at the corresponding
phase are at their full-scale input level. The average active power
is divided by the content of the watt divider register before it is
added to the corresponding watt-hr accumulation registers.
When the value in the WDIV[7:0] register is 0 or 1, active
power is accumulated without division. WDIV is an 8-bit
unsigned register that is useful to lengthen the time it takes
before the watt-hr accumulation registers overflow.
Figure 67 shows the energy accumulation for full-scale signals
(sinusoidal) on the analog inputs. The three displayed curves
show the minimum time it takes for the watt-hr accumulation
register to overflow when the watt gain register of the corre-
sponding phase equals to 0x7FF, 0x000, and 0x800. The watt
gain registers are used to carry out a power calibration in the
ADE7758. As shown, the fastest integration time occurs when
the watt gain registers are set to maximum full scale, that is, 0x7FF.
Energy
=
V
0xD7AE14
∫
0x2851EC
I
p
0xD7AE
0x2852
( )
CURRENT SIGNAL–i(t)
VOLTAGE SIGNAL–v(t)
t
0x00
000x
dt
PHCAL[6:0]
HPF
=
Lim
T
Φ
→
0
INTEGRATOR
⎧
⎨
⎩
n
∑
DIGITAL
∞
=
0
p
( )
nT
0xCCCCD
0x00000
×
MULTIPLIER
T
⎫
⎬
⎭
Figure 66. ADE7758 Active Energy Accumulation
SIGN 2
AVERAGE POWER
SIGNAL–P
LPF2
T
6
AWATTOS[11:0]
(20)
Rev. D | Page 32 of 72
+
2
0
TIME (nT)
+
2
–1
AWG[11:0]
2
–2
2
This is the time it takes before overflow can be scaled by writing
to the WDIV register and therefore can be increased by a
maximum factor of 255.
Note that the active energy register content can roll over to full-
scale negative (0x8000) and continue increasing in value when
the active power is positive (see Figure 66). Conversely, if the
active power is negative, the energy register would under flow
to full-scale positive (0x7FFF) and continue decreasing in value.
By setting the AEHF bit (Bit 0) of the interrupt mask register,
the ADE7758 can be configured to issue an interrupt ( IRQ )
when Bit 14 of any one of the three watt-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 watt-hr accumulation registers,
that is, the registers are reset to 0 after a read operation.
WDIV[7:0]
–3
ACCUMULATION REGISTER
%
2
CONTENTS OF WATT-HR
–4
Figure 67. Energy Register Roll-Over Time for Full-Scale Power
0x7FFF
0x3FFF
0xC000
0x0000
0x8000
+
+
40
15
(Minimum and Maximum Power Gain)
AWATTHR[15:0]
0.13
TOTAL ACTIVE POWER IS
ACCUMULATED (INTEGRATED) IN
THE ACTIVE ENERGY REGISTER
0.52
0.79
TIME (Sec)
0
1.05
1.31
WATT GAIN = 0x7FF
WATT GAIN = 0x000
WATT GAIN = 0x800
1.58
0