ADE7754AR Analog Devices Inc, ADE7754AR Datasheet - Page 20

• Manufacturer Part Number: ADE7754AR
• Description: IC ENERY METER 3PHASE 24-SOIC
• Manufacturer: Analog Devices Inc

Specifications of ADE7754AR

• Input Impedance: 370 KOhm
• Measurement Error: 0.1%
• Voltage - I/o High: 2.4V
• Voltage - I/o Low: 0.8V
• Current - Supply: 7mA
• 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
• For Use With: EVAL-ADE7754EBZ - BOARD EVALAUTION FOR ADE7754
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: AD71049AR; AD71049AR

ADE7754
The discrete time sample period (T) for the accumulation
register in the ADE7754 is 0.4 µs (4/10 MHz). In addition to
calculating the energy, this integration removes any sinusoidal
component that may be in the active power signal. Figure 27
shows a graphical representation of this discrete time integration
or accumulation. The active power signal is continuously added
to the internal energy register. Because this addition is a signed
addition, negative energy will be subtracted from the active
energy contents.
The 54-bit value of the internal energy register is divided by
WDIV. If the value in the WDIV register is 0, then the internal
active energy register is divided by 1. WDIV is an 8-bit unsigned
register. The upper 24-bits of the result of the division are then
available in the 24-bit active energy register. The AENERGY
and RAENERGY registers read the same internal active energy
register. They differ by the state in which they are leaving the
internal active energy register after a read. Two operations are
held when reading the RAENERGY register: read and reset to 0
the internal active energy register. Only one operation is held
when reading the AENERGY register: read the internal active
energy register.
Figure 28 shows the energy accumulation for full-scale (sinusoidal)
signals on the analog inputs. The three displayed curves illustrate
the minimum time it takes the energy register to roll over when
the individual watt gain registers contents are all equal to 3FFh,
000h, and 800h. The watt gain registers are used to carry out a
power calibration in the ADE7754. As shown, the fastest
integration time occurs when the watt gain registers are set to
maximum full scale, i.e., 3FFh.
TOTAL ACTIVE POWER
26667h
00000h
Figure 27. Active Energy Calculation
T
T
TIME (nT)
ACTIVE POWER
SIGNAL (P)
+
+
WDIV
53
53
23
AENERGY[23:0]
TOTAL ACTIVE POWER IS
ACCUMULATED (INTEGRATED) IN
THE ACTIVE ENERGY REGISTER
%
0
0
0
–20–
Note that the active energy register contents roll over to full-
scale negative (80,0000h) and continue increasing in value
when the power or energy flow is positive. See Figure 28.
Conversely, if the power is negative, the energy register would
underflow to full scale positive (7F,FFFFh) and continue
decreasing in value.
By using the interrupt enable register, the ADE7754 can be
configured to issue an interrupt (IRQ) when the active energy
register is half full (positive or negative).
Integration Times Under Steady Load
As mentioned in the last section, the discrete time sample
period (T) for the accumulation register is 0.4 µs (4/CLKIN).
With full-scale sinusoidal signals on the analog inputs and the
watt gain registers set to 000h, the average word value from
each LPF2 is D1B717h. See Figures 22 and 24. The maximum
value that can be stored in the active energy register before it
overflows is 2
added to the internal register, which can store 2
1F,FFFF,FFFF,FFFFh before it overflows, the integration time
under these conditions with WDIV = 0 is calculated as follows:
When WDIV is set to a value different from 0, the integration
time varies as shown in Equation 10.
The WDIV register can be used to increase the time before the
active energy register overflows, thereby reducing the communi-
cation needs with the ADE7754.
Energy to Frequency Conversion
The ADE7754 also provides energy-to-frequency conversion
for calibration purposes. After initial calibration at manufac-
ture, the manufacturer or the customer will often verify the
energy meter calibration. One convenient way to verify the
meter calibration is for the manufacturer to provide an output
frequency proportional to the energy or active power under
steady load conditions. This output frequency can provide a
simple single-wire, optically isolated interface to external cali-
bration equipment. Figure 29 illustrates the energy to frequency
conversion in the ADE7754.
7F,FFFFh
3F,FFFFh
00,0000h
40,0000h
80,0000h
AENERGY[23:0]
Time
Time Time
Figure 28. Energy Register Roll-Over Time for Full-
Scale Power (Minimum and Maximum Power Gain)
=
=
1
44
23
F FFFF FFFF FFFFh
– 1 or 7F,FFFFh. As the average word value is
,
WDIV
88
3
TIME (sec)
= 0
×
132
D B
,
×
1 717
WDIV
176
220
,
h
264
×
0 4
. µ
AWG = BWG = CWG = 3FFh
AWG = BWG = CWG = 000h
AWG = BWG = CWG = 800h
s
=
53
88
– 1 or
s
REV. 0
(10)