Datasheet

Industrial V/I Converter and Protector IC
AM462
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz Oktober 2007 – Rev.2.5 -Page 8/20
Phone: [phone]
Fax: [phone]
Internet:
http://www.analogmicro.de
Email: info@analogmicro
.de
INITIAL OPERATION OF AM462
General information on 2- and 3-wire applications and the use of current
In 3-wire operation (cf. Figure 3 right and Figure 7) the ground of the IC (pin GND) is connected up
to the external mass of the system Ground. The system's supply voltage V
S
is connected to pin VCC
and pin VCC to pin RS+.
In 2-wire operation (cf. Figure 3 left and Figure 7) system supply voltage V
S
is connected to pin
RS+ and pin VCC to 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 resistor R
L
which connects current output I
OUT
to
the system ground.
In 2-wire operation the IC ground is "virtual" (floating), as with a constant load resistance the
supply voltage of the device V
CC
changes according to the current. As a rule, the following equation
applies to 2-wire operation:
()
LINOUTSCC
RVIVV −= (3)
The reason for this is that in 2-wire operation the IC is connected in series to the actual load resistor
R
L
. This is illustrated in Figure 3.
In 3-wire operation V
CC
= V
S
, as the IC ground is connected to the ground of the system.
Setting the output current range
When using amplification stage OP1 together with the V/I converter for voltage-to-current
conversion the offset of the output current should first be compensated for by suitable selection of
resistors R
3
and R
4
. To this end the OP1 input must be connected to ground (V
INP
= 0). With the
short circuit at the input and by connecting up V/I converter pin VSET as shown in Figure 2 the
values of the output current according to Equation 2 are as follows:
R
L
V
S
2-wire system
signal source and
conditioning IC
GND Ground ≠
V
CC
≠ V
S
Ground
R
L
3-wire system
signal source and
conditioning IC
GND Ground =
V
CC
= V
S
Ground GND =
GND
V
CC
I
OUT
I
OUT
VV
CC S
=
Figure 3: The difference between 2- and 3-wire operation