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ISO212P
9
FIGURE 6. Oscillator Connections for Synchronous Opera-
tion in Multiple ISO212P Installations.
APPLICATIONS FLEXIBILITY
In Figure 8, the ISO212P’s +V
ss 1
isolated supply powers a
REF200 to provide an accurate 100
μ
A current source. This
current is opposed by an equal but opposite current through
the 75k
feedback resistor to establish an offset of –7.5V at
I
in
= 0mA. With I
in
= 4-to-20mA, the output is –5 to +5V.
The ratio of the 75k
and 3.12k
resistors assures the
correct gain.
The polarity of the output can be reversed by simply revers-
ing the O/P HI and O/P LO pins. This could be used in the
Figure 8 circuit to change the –5V to +5V output to a +5V
to –5V output range.
The primary function of the output circuitry is to add gain to
produce a
±
10V output and to reduce output impedance. The
addition of a few resistors and capacitors provides a low pass
filter with a cut-off frequency equal to the full signal
bandwidth of the ISO212P, typically 200Hz. The filter
response is flat to 1dB and rolls off from cut off at –12dB per
octave.
The accuracy of the REF200 and external resistors elimi-
nates the need for expensive trim pots and adjustments. The
errors introduced by the external circuitry only add about
10% of the ISO212P’s specified gain and offset voltage
error.
FIGURE 8. Isolated 4-20mA Current Receiver with Output Filter.
FIGURE 7. Isolating the Clk Out Node.
2
6
10μF
0.1μF
0.1μF
0.1μF
22k
22k
4-20mA
8
1
3.12k
75k
25
+V
SS 1
ISO212P
+
–
31
32
38 (O/P High)
37 (O/P Low)
100k
100k
(5%)
(5%)
6.8nF
(10%)
6.8nF (10%)
+15V
6
–15V
4mA to 20mA
–10V to +10V
+15V
+V
SS 1
4
1
3
4mA to 20mA
–5V to +5V
+
OPA27
–
REF
200
0.02μF
3
2
NOTE: All resistors are 0.1%
unless otherwise stated.
100μA
0V +15V Sync
+V
Clk Out
Clk In
Com 2
CC
ISO212P/Slave
+V
Clk Out
Clk In
Com 2
CC
ISO212P/Slave
+V
Clk Out
Clk In
Com 2
CC
ISO212P/Master
Clk Out
Clk In
Clk In
Clk In
Clk In
S
R
S
22k
22k
22k
22k
22k
S
S
S
S
M
Clk Out
Clk In
Clk In
Clk In
Clk In
S
S
S
S
S
M