AD7755AAN Analog Devices Inc, AD7755AAN Datasheet - Page 11

• Manufacturer Part Number: AD7755AAN
• Manufacturer: Analog Devices Inc

Specifications of AD7755AAN

• Operating Temperature (max): 85C
• Operating Temperature (min): -40C
• Pin Count: 24
• Mounting: Through Hole
• Package Type: PDIP
• Screening Level: Industrial
• Lead Free Status / Rohs Status: Not Compliant

Using Equations 1 and 2, the real power P can be expressed in
terms of its fundamental real power (P
power (P
where:
and
As can be seen from Equation 4 above, a harmonic real power
component is generated for every harmonic, provided that har-
monic is present in both the voltage and current waveforms.
The power factor calculation has previously 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 a master clock frequency of 3.5795 MHz.
ANALOG INPUTS
Channel V1 (Current Channel )
The voltage output from the current transducer is connected to
the AD7755 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 1 should be
less than 470 mV (330 mV rms for a pure sinusoidal signal) for
specified operation. Note that Channel 1 has a programmable
gain amplifier (PGA) with user selectable gain of 1, 2, 8 or 16
(see Table I). These gains facilitate easy transducer interfacing.
The diagram in Figure 22 illustrates the maximum signal levels
on V1P and V1N. The maximum differential voltage is 470 mV
divided by the gain selection. 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 22.
+470mV
–470mV
P
P
1
1
h
H
V
CM
H
V
).
V1
h 1
1
1
h
–
Vh
–
I
1
1
cos
h
Ih
1
cos
DIFFERENTIAL INPUT
P
470mV MAX PEAK
COMMON-MODE
h
P
100mV MAX
1
P
H
1
) and harmonic real
AGND
V1
V
CM
V1P
V1N
(3)
(4)
G1
0
0
1
1
Channel V2 (Voltage Channel )
The output of the line voltage transducer is connected to the
AD7755 at this analog input. Channel V2 is a fully differential
voltage input. The maximum peak differential signal on Chan-
nel 2 is 660 mV. Figure 23 illustrates the maximum signal
levels that can be connected to the AD7755 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
AD7755 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.
Typical Connection Diagrams
Figure 24 shows a typical connection diagram for Channel V1.
A CT (current transformer) is the current transducer selected for
this example. Notice the common-mode voltage for Channel 1
is AGND and is derived by center tapping the burden resistor
to AGND. This provides the complementary analog input sig-
nals for V1P and V1N. The CT turns ratio and burden resistor
Rb are selected to give a peak differential voltage of 470 mV/
Gain at maximum load.
IP
PHASE
+660mV
–660mV
V
CM
NEUTRAL
V2
G0
0
1
0
1
Table I. Gain Selection for Channel 1
AGND
CT
DIFFERENTIAL INPUT
Gain
1
2
8
16
660mV MAX PEAK
Rb
COMMON-MODE
100mV MAX
Rf
Rf
470mV
GAIN
Maximum
Differential Signal
AGND
470 mV
235 mV
60 mV
30 mV
V2
V
CM
Cf
Cf
V2P
AD7755
V2N
V1P
V1N