ADE7755ARSZRL Analog Devices Inc, ADE7755ARSZRL Datasheet - Page 12

• Manufacturer Part Number: ADE7755ARSZRL
• Description: Energy Metering IC With Pulse Output
• Manufacturer: Analog Devices Inc

Specifications of ADE7755ARSZRL

• 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: Surface Mount
• Package / Case: 24-SSOP (0.200", 5.30mm Width)
• Meter Type: Single Phase
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: EVAL-ADE7755ZEB - BOARD EVALUATION FOR AD7755
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

ADE7755
THEORY OF OPERATION
The two ADCs of the ADE7755 digitize the voltage signals from
the current and voltage transducers. These ADCs are 16-bit,
second-order Σ-Δ with an oversampling rate of 900 kHz. This
analog input structure greatly simplifies transducer interfacing
by providing a wide dynamic range for direct connection to the
transducer and also by simplifying the antialiasing filter design.
A programmable gain stage in the current channel further
facilitates easy transducer interfacing. A high-pass filter in the
current channel removes any dc components from the current
signal. This removal eliminates any inaccuracies in the active
power calculation due to offsets in the voltage or current signals
(see the HPF and Offset Effects section).
The active power calculation is derived from the instantaneous
power signal. The instantaneous power signal is generated by a
direct multiplication of the current and voltage signals. To
extract the active power component (that is, the dc component),
the instantaneous power signal is low-pass filtered. Figure 22
illustrates the instantaneous active power signal and shows how
the active power information can be extracted by low-pass filtering
the instantaneous power signal. This scheme correctly calculates
active power for nonsinusoidal current and voltage waveforms
at all power factors. All signal processing is carried out in the
digital domain for superior stability over temperature and time.
V × I
V × I
The low frequency output of the ADE7755 is generated by
accumulating this active power information. This low frequency
inherently means a long accumulation time between output
pulses. The output frequency is therefore proportional to the
average active power. This average active power information
can, in turn, be accumulated (for example, by a counter) to
generate active energy information. Because of its high output
frequency and shorter integration time, the calibration frequency
(CF) output is proportional to the instantaneous active power.
This is useful for system calibration purposes that take place
under steady load conditions.
CH1
CH2
2
PGA
TIME
POWER SIGNAL {p(t)}
INSTANTANEOUS
Figure 22. Signal Processing Block Diagram
ADC
ADC
p(t) = i(t) × v(t)
WHERE:
MULTIPLIER
v(t) = V × cos(ωt)
i(t) = I × cos(ωt)
p(t) =
HPF
V × I
2
{1+cos (2ωt)}
LPF
V × I
2
INSTANTANEOUS ACTIVE
POWER SIGNAL
FREQUENCY
DIGITAL-TO-
FREQUENCY
DIGITAL-TO-
F1
F2
CF
Rev. A | Page 12 of 20
POWER FACTOR CONSIDERATIONS
The method used to extract the active power information from
the instantaneous power signal (that is, by low-pass filtering) is
valid even when the voltage and current signals are not in phase.
Figure 23 displays the unity power factor condition and a
displacement power factor (DPF) = 0.5, that is, current signal
lagging the voltage by 60°. Assuming that the voltage and current
waveforms are sinusoidal, the active power component of the
instantaneous power signal (that is, the dc term) is given by
This is the correct active power calculation.
V × I
2
cos(60°)
Figure 23. DC Component of Instantaneous Power Signal Conveys
⎛
⎜
⎝
V
V × I
2
2
0V
0V
×
I
⎞
⎟
⎠
×
INSTANTANEOUS
POWER SIGNAL
cos
INSTANTANEOUS
VOLTAGE
CURRENT
VOLTAGE
POWER SIGNAL
Active Power Information PF < 1
(
60
°
)
60°
INSTANTANEOUS ACTIVE
INSTANTANEOUS ACTIVE
POWER SIGNAL
POWER SIGNAL
CURRENT