Datasheet

Industrial Converter and Protector IC AM460
analog microelectronics
April 2003
14/18
Typical 2-wire application with an input signal referenced to ground
In 2-wire operation (cf. Figure 8) system supply voltage V
S
is connected up to pin RS+ and pin VCC to pin RS-.
The ground of the IC (pin GND) is connected to the node between resistor R
5
and load resistor R
L
(current output
I
OUT
). IC ground (GND) is not the same as system ground (Ground)!! The output signal is picked up via load re-
sistor R
L
which connects current output I
OUT
to the system ground.
For output current I
OUT
the following applies according to Equation 3:
SET
I
INPOUT
I
R
G
VI +⋅=
0
8
with
2
1
1
R
R
GG
GAINI
+==
and
43
4
0
2 RR
R
R
V
I
REF
SET
+
⋅=
Example 4:
To obtain a signal of V
INP
= 0...1V at the OP1 input the external components are to be dimensioned in such a
way that the output current has a range of 4...20mA.
mA4
88
00
+⋅=+⋅=
R
G
VI
R
G
VI
GAIN
INPSET
I
INPOUT
With R
0
= 27Ω Equation 7 produces the following:
15.221
mA4272
V5
1
2
04
3
≈−
⋅Ω⋅
=−=
SET
REF
IR
V
R
R
and thus the following value for the gain to be set:
Ground
T
1
D
1
R
5
R
L
1
Single-ended
input voltage
1
2
AM460
OP3
OP2
R
1
R
2
4
OP1
5
3
R
3
C
1
Voltage Reference
R
0
7146
13
15
16
IC ground: GND
System ground: Ground
}
Different
potentials!
GND
2-wire
connection
C
2
12
8
9
11
10
V
R
4
I
V
INP
V
S
I
OUT
V
BG
Connections setting unused function blocks to a defined operating point
Figure 8: Typical 2-wire application for input signals referenced to ground