ADE7751AAN-REF Analog Devices, ADE7751AAN-REF Datasheet - Page 11

• Manufacturer Part Number: ADE7751AAN-REF
• Description: Energy Metering IC with On-Chip Fault Detection
• Manufacturer: Analog Devices

Using Equations 2 and 3, the real power P can be expressed in
terms of its fundamental real power (P
power (P
where:
and
As shown in Equation 5 above, a harmonic real power compo-
nent is generated for every harmonic, provided that harmonic is
present in both the voltage and current waveforms. The power
factor calculation has been shown previously to be accurate in
the case of a pure sinusoid, therefore the harmonic real power
must also correctly account for the power factor since it is made
up of a series of pure sinusoids.
Note that the input bandwidth of the analog inputs is 14 kHz
with a master clock frequency of 3.5795 MHz.
ANALOG INPUTS
Channel V2 (Voltage Channel)
The output of the line voltage transducer is connected to the
ADE7751 at this analog input. Channel V2 is a fully differen-
tial voltage input. The maximum peak differential signal on
Channel 2 is 660 mV. Figure 4 illustrates the maximum
signal levels that can be connected to the ADE7751 Channel 2.
Channel 2 must be driven from a common-mode voltage, i.e.,
the differential voltage signal on the input must be referenced to
a common mode (usually AGND). The analog inputs of the
ADE7751 can be driven with common-mode voltages of up to
100 mV with respect to AGND. However, best results are
achieved using a common mode equal to AGND.
Channel V1 (Current Channel)
The voltage outputs from the current transducers are connected
to the ADE7751 here. Channel V1 has two voltage inputs, namely
V1A and V1B. These inputs are fully differential with respect to
V1N. However, at any one time, only one is selected to perform
the power calculation—see Fault Detection section.
REV. 0
+600mV
–600mV
P
P
1
1
H
h
Figure 4. Maximum Signal Levels, Channel 2
V
H
CM
V
).
V2
1
h 1
1
h
–
–
V
I
1
1
h
cos( )
h
I
h
1
cos( )
DIFFERENTIAL INPUT
P = P
600mV MAX PEAK
COMMON MODE
h
100mV MAX
1
+ P
H
AGND
1
) and harmonic real
V2
V
CM
V2P
V2N
(4)
(5)
–11–
The analog inputs V1A, V1B, and V1N have the same maximum
signal level restrictions as V2P and V2N. However, Channel 1
has a programmable gain amplifier (PGA) with user-selectable
gains of 1, 2, 8, or 16—see Table I. These gains facilitate easy
transducer interfacing.
Figure 5 illustrates the maximum signal levels on V1A, V1B,
and V1N. The maximum differential voltage is 660 mV divided
by the gain selection. Again, the differential voltage signal on the
inputs must be referenced to a common mode, e.g., AGND. The
maximum common-mode signal is 100 mV as shown in Figure 5.
G1
0
0
1
1
Typical Connection Diagrams
Figure 6 shows a typical connection diagram for Channel V1.
Here the analog inputs are being used to monitor both the
phase and neutral currents. Because of the large potential
difference between the phase and neutral, two CTs (current
transformers) must be used to provide the isolation. Notice
both CTs are referenced to AGND (analog ground), hence
the common-mode voltage is 0 V. The CT turns ratio and
burden resistor (Rb) are selected to give a peak differential
voltage of 660 mV/gain.
IP
+660mV
–660mV
PHASE
GAIN
GAIN
V
V1A, V1B
CM
Figure 5. Maximum Signal Levels, Channel 1
Figure 6. Typical Connection for Channel 1
IN
NEUTRAL
G0
0
1
0
1
AGND
DIFFERENTIAL INPUT A
DIFFERENTIAL INPUT B
CT
CT
660mV/GAIN MAX PEAK
COMMON MODE
660mV/GAIN MAX PEAK
100mV MAX
Rb
Rb
Table I.
Gain
1
2
8
16
GAIN
660mV
GAIN
660mV
AGND
R f
R f
V
CM
Maximum
Differential Signal
V1
V1
660 mV
330 mV
82 mV
41 mV
C f
C f
ADE7751
V1A
V1N
V1B
V1A
V1N
V1B