ADE7757 Analog Devices, ADE7757 Datasheet - Page 9

• Manufacturer Part Number: ADE7757
• Description: Energy Metering IC with Integrated Oscillator
• Manufacturer: Analog Devices

Using Equations 1 and 2, the real power P can be ex-
pressed in terms of its fundamental real power (P
harmonic real power (P
where:
and
As can be seen from Equation 4 above, a harmonic real
power component is generated for every harmonic, pro-
vided that harmonic is present in both the voltage and
current waveforms. The power factor calculation has pre-
viously been shown to be accurate in the case of a pure
sinusoid, therefore the harmonic real power must also
correctly account for 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.
The voltage output from the current sensor is connected to the
ADE7757 here. Channel V1 is a fully differential voltage input.
V1P is the positive input with respect to V1N.
The maximum peak differential signal on Channel V1 should
be less than ±30 mV (21 mV rms for a pure sinusoidal signal)
for specified operation.
The diagram in Figure 13 illustrates the maximum signal
levels on V1P and V1N. The maximum differential voltage
is ±30 mV. The differential voltage signal on the inputs
must be referenced to a common mode, e.g. AGND. The
maximum common mode signal is ±6.25 mV as shown in
Figure 13.
REV. PrC.
P
P
1
1
H
h
+30mV
-30mV
V
CM
V
h
V1
1
1
h
1
V
I
h
1
1
cos
h
I
h
cos
1
DIFFERENTIAL INPUT
H
P
h
).
30mV MAX PEAK
COMMON-MODE
PRELIMINARY TECHNICAL DATA
P
6.25mV MAX
1
P
H
AGND
V1
V
CM
V1P
V1N
1
) and
(3)
(4)
– 9 –
The output of the line voltage sensor is connected to the
ADE7757 at this analog input. Channel V2 is a fully differen-
tial voltage input with maximum peak differential signal
of ±165 mV. Figure 14 illustrates the maximum signal
levels that can be connected to the ADE7757 Channel V2.
Channel V2 is usually driven from a common-mode volt-
age, i.e., the differential voltage signal on the input is
referenced to a common mode (usually AGND). The
analog inputs of the ADE7757 can be driven with com-
mon-mode voltages of up to 25 mV with respect to
AGND. However best results are achieved using a com-
mon mode equal to AGND.
Figure 15 shows a typical connection diagram for Channel V1.
A shunt is the current sensor selected for this example because of
its low cost compared to other current sensors such as the CT
(current transformer). This IC is ideal for low current
meters.
Figure 16 shows a typical connection for Channel V2.
Typically, ADE7757 is biased around the neutral wire,
and a resistor divider is used to provide a voltage signal
that is proportional to the line voltage. Adjusting the ratio
of Ra, Rb and VR is also a convenient way of carrying out
a gain calibration on a meter.
PHASE
+165mV
-165mV
PHASE
V
CM
NEUTRAL
V2
SHUNT
AGND
NEUTRAL
Ra *
VR *
Rb *
* Ra >> Rf + VR
* Rb + VR = Rf
DIFFERENTIAL INPUT
Cf
165mV
165mV MAX PEAK
COMMON-MODE
Rf
Rf
30mV
25mV MAX
AGND
Cf
Cf
Rf
V2
V
CM
V1P
V1N
Cf
V2P
V2N
V2P
V2N