Datasheet

AD71056
Rev. A | Page 12 of 20
APPLICATIONS
ANALOG INPUTS
Channel V1 (Current Channel)
The voltage output from the current sensor is connected to the
AD71056 at Channel V1. 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.
+30mV
–30mV
V
CM
V
1
DIFFERENTIAL INPUT
±30mV MAX PEAK
COMMON MODE
±6.25mV MAX
V1P
V1N
V1
V
CM
AGND
05636-017
Figure 17. Maximum Signal Levels, Channel V1
Figure 17 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, such as AGND. The maximum common-mode
signal is ±6.25 mV, as shown in Figure 17.
Channel V2 (Voltage Channel)
The output of the line voltage sensor is connected to the
AD71056 at Channel V2. Channel V2 is a fully differential
voltage input with a maximum peak differential signal of ±165 mV.
Figure 18 illustrates the maximum signal levels that can be
connected to the AD71056 Channel V2.
+165m
V
–
165mV
V
CM
V
2
DIFFERENTIAL INPUT
±165mV MAX PEAK
COMMON MODE
±25mV MAX
V2P
V2N
V2
V
CM
AGND
05636-018
Figure 18. Maximum Signal Levels, Channel V2
Channel V2 is usually driven from a common-mode voltage,
that is, the differential voltage signal on the input is referenced
to a common mode (usually AGND). The analog inputs of the
AD71056 can be driven with common-mode voltages of up
to 25 mV with respect to AGND. However, best results are
achieved using a common mode equal to AGND.
Typical Connection Diagrams
Figure 19 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
current transformer (CT). This IC is ideal for low current meters.
V
1P
V1N
C
F
C
F
R
F
R
F
±30mV
SHUNT
AGND
PHASE NEUTRAL
05636-019
Figure 19. Typical Connection for Channel V1
Figure 20 shows a typical connection for Channel V2. Typically,
the AD71056 is biased around the phase wire and a resistor
divider is used to provide a voltage signal that is proportional to
the line voltage. Adjusting the ratio of R
A
, R
B
, and R
F
is also a
convenient way of carrying out a gain calibration on a meter.
V2P
V2N
C
F
PHASENEUTRAL
R
F
±165mV
C
F
R
F
R
B
R
A
1
1
R
A
>> R
B
+ R
F
.
05636-020
Figure 20. Typical Connections for Channel V2