ADE7768ARZ-RL Analog Devices Inc, ADE7768ARZ-RL Datasheet - Page 10

• Manufacturer Part Number: ADE7768ARZ-RL
• Description: IC,Power Metering,CMOS,SOP,16PIN,PLASTIC
• Manufacturer: Analog Devices Inc

Specifications of ADE7768ARZ-RL

• Input Impedance: 320 KOhm
• Measurement Error: 0.1%
• Voltage - I/o High: 2.4V
• Voltage - I/o Low: 0.8V
• Current - Supply: 5mA
• Voltage - Supply: 4.75 V ~ 5.25 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (0.154", 3.90mm Width)
• Meter Type: Single Phase
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

ADE7768
FUNCTIONAL DESCRIPTION
THEORY OF OPERATION
The two ADCs in the ADE7768 digitize the voltage signals from
the current and voltage sensors. These ADCs are 16-bit Σ-Δs
with an oversampling rate of 450 kHz. This analog input
structure greatly simplifies sensor interfacing by providing a
wide dynamic range for direct connection to the sensor and
by simplifying the antialiasing filter design. A high-pass filter
in the current channel removes any dc component from the
current signal. This eliminates any inaccuracies in the real
power calculation due to offsets in the voltage or current
signals.
The real 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 real power component (the dc component), the
instantaneous power signal is low-pass filtered. Figure 15
illustrates the instantaneous real power signal and shows how
the real power information can be extracted by low-pass
filtering the instantaneous power signal. In the ADE7768,
this signal is compared to 0 and only positive real power is
accumulated for F1, F2, and CF pulse outputs. This scheme
correctly calculates real power for sinusoidal 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.
The low frequency outputs (F1 and F2) are generated by
accumulating positive-only real power information. This low
frequency inherently means a long accumulation time between
output pulses. Consequently, the resulting output frequency is
proportional to the average positive-only real power. This
average positive-only real power information is then accumu-
lated (by a counter) to generate real energy information (see
Figure 16). Conversely, due to its high output frequency and
shorter integration time, the CF output frequency is propor-
tional to the instantaneous positive-only real power. This is
useful for system calibration, which can be done faster under
steady load conditions.
CH1
CH2
TIME
POWER SIGNAL – p(t)
INSTANTANEOUS
Figure 15. Signal Processing Block Diagram
ADC
ADC
MULTIPLIER
HPF
LPF
≥0
INSTANTANEOUS REAL
POWER SIGNAL
TIME
FREQUENCY
DIGITAL-TO-
FREQUENCY
DIGITAL-TO-
Rev. A | Page 10 of 20
F1
F2
CF
Power Factor Considerations
The method used to extract the real power information from
the instantaneous power signal (that is, by low-pass filtering) is
still valid even when the voltage and current signals are not in
phase. Figure 17 displays the unity power factor condition and a
displacement power factor (DPF) = 0.5 (a current signal lagging
the voltage by 60°). Assuming that the voltage and current
waveforms are sinusoidal, the real power component of the
instantaneous power signal (that is, the dc term) is given by
This is the correct real power calculation.
V × I
2
0Wh
0W
COS (60°)
Figure 17. DC Component of Instantaneous Power Signal Conveys
⎛
⎜
⎝
V
V × I
ACTIVE ENERGY
INSTANTANEOUS
POWER
2
2
×
POWER
POWER
0V
0V
I
⎞
⎟
⎠
VOLTAGE
Figure 16. Positive-Only Energy Accumulation
×
INSTANTANEOUS
POWER SIGNAL
cos
INSTANTANEOUS
CURRENT
VOLTAGE
POWER SIGNAL
(
Real Power Information, PF < 1
60
°
)
60°
INSTANTANEOUS REAL
POWER SIGNAL
INSTANTANEOUS REAL
POWER SIGNAL
CURRENT
TIME
TIME
(1)