ADE7756AN Analog Devices Inc, ADE7756AN Datasheet - Page 22

• Manufacturer Part Number: ADE7756AN
• Description: IC ENERGY METERING 20-DIP
• Manufacturer: Analog Devices Inc

Specifications of ADE7756AN

• Rohs Status: RoHS non-compliant
• Input Impedance: 390 KOhm
• Measurement Error: 0.1%
• Voltage - I/o High: 2.4V
• Voltage - I/o Low: 0.8V
• Current - Supply: 3mA
• Voltage - Supply: 4.75 V ~ 5.25 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Through Hole
• Package / Case: 20-DIP (0.300", 7.62mm)
• Meter Type: Single Phase
• Lead Free Status / RoHS Status: Not Compliant

ADE7756
ENERGY CALCULATION
As stated earlier, power is defined as the rate of energy flow.
This relationship can be expressed mathematically as Equation 5.
where
Conversely, Energy is given as the integral of Power.
The ADE7756 achieves the integration of the Active Power signal
by continuously accumulating the Active Power signal in the 40-bit
Active Energy register (AENERGY[39:0]). This discrete time
accumulation or summation is equivalent to integration in con-
tinuous time. Equation 7 expresses the relationship
where
and
The discrete time sample period (T) for the accumulation regis-
ter in the ADE7756 is 1.1 µs (4/CLKIN). As well as calculating
the Energy, this integration removes any sinusoidal components
that may be in the Active Power signal.
Figure 30 shows a graphical representation of this discrete time
integration or accumulation. The Active Power signal in the
Waveform register is continuously added to the Active Energy
register. This addition is a signed addition, therefore negative
energy will be subtracted from the Active Energy contents.
As shown in Figure 30, the Active Power signal is accumulated
in a 40-bit signed register (AENERGY[39:0]).
CHANNEL
CURRENT
CHANNEL
VOLTAGE
P = Power, and
E = Energy.
n is the discrete time sample number
T is the sample period.
P
E
E
=
= ∫
= ∫
dE
dt
p t dt
Pdt
( )
ACTIVE POWER
T
20
=
SIGNAL – P
Lim
T
LPF2
CLKIN
→
TIME – nT
4
0



n
∑
∞
=
0
WAVEFOR
REGISTER
VALUES
11
p nT
(
23
39
)
×
T
WAVEFORM REGISTER VALUES ARE
ACCUMULATED (INTEGRATED) IN
THE ACTIVE ENERGY REGISTER
WAVEFORM [23:0]



AENERGY[39:0]
APOS [11:0]
0
0
0
(5)
(6)
(7)
The Active Power signal can be read from the Waveform regis-
ter by setting MODE[14:13] = 0,0 and setting the WSMP bit
(Bit 3) in the Interrupt Enable register to 1. Like the Channel 1
and Channel 2 waveform sampling modes, the waveform date
is available at sample rates of 27.9 kSPS, 14 kSPS, 7 kSPS or
3.5 kSPS—see Figure 19.
Figure 31 shows this energy accumulation for full-scale signals
(sinusoidal) on the analog inputs. The three curves displayed,
illustrate the minimum period of time it takes the energy register
to roll-over when the Active Power Gain register contents are
3FFh, 000h and 800h. The Active Power Gain register is used
to carry out power calibration in the ADE7756. As shown, the
fastest integration time will occur when the Active Power Gain
register is set to maximum full scale, i.e., 3FFh.
Note that the energy register contents will roll over to full-scale
negative (80,0000,0000h) and continue increasing in value when
the power or energy flow is positive—see Figure 31. Conversely,
if the power is negative the energy register would underflow to
full-scale positive (7F, FFFF, FFFFh) and continue decreasing
in value.
By using the Interrupt Enable register, the ADE7756 can be
configured to issue an interrupt (IRQ) when the Active Energy
register is half-full (positive or negative) or when an over-/under-
flow occurs.
Integration Times under Steady Load
As mentioned in the last section, the discrete time sample
period (T) for the accumulation register is 1.1 µs (4/CLKIN).
With full-scale sinusoidal signals on the analog inputs and the
Active Power Gain register set to 000h, the average word value
from LPF2 is CCCDh—see Figure 34. The maximum value
that can be stored in the Active Energy register before it over-
flows is 2
time under these conditions is calculated as follows:
7F,FFFF,FFFFh
3F,FFFF,FFFFh
00,0000,0000h
40,0000,0000h
80,0000,0000h
Time
39
or 7F, FFFF, FFFFh. Therefore the integration
=
AENERGY[39:0]
7
F FFFF FFFFh
,
CCCDh
5.8s
,
11.5s
×
1 1
.
23s
µ
s
=
11 53
.
APGAIN = 3FFh
APGAIN = 000h
APGAIN = 800h
TIME
(SECONDS)
seconds