Industrial Converter and Protector IC
AM460
reduce power dissipation the transistor is an external component and protected against reverse polarity by an
additional diode
D
1
. Via pin
SET
an offset current
I
SET
can be set at output
IOUT
(with the help of the inter-
nal voltage reference and an external voltage divider as shown in Figure 2, for example). External resistor
R
0
permits the output current to be finely adjusted with parallel operation of current and the voltage output. For
the output current provided by
T
1
the following ratio applies:
I
OUT
=
V
V
INDAI
+
I
SET
with
I
SET
=
SET
8
R
0
2R
0
(3)
with
V
INDAI
the voltage at
INDAI
and
V
SET
the voltage at pin
SET
(V/I converter inputs, Figure 2)
.
4. The AM460
reference voltage source
enables voltage to be supplied to external components (such as sen-
sors, microprocessors, etc.). The reference voltage value
V
REF
can be set via pin 13
VSET.
If pin
VSET
is not
connected,
V
REF
= 5V; if
VSET
is switched to ground,
V
REF
= 10V. Values between these can be set if two
external resistors are used (inserted between pin
VREF
and pin
VSET
and between pin
VSET
and
GND).
External (ceramic) capacitor
C
1
at pin
VREF
stabilises the reference voltage. It
must
be connected even if
the voltage reference is not in use.
5. The additional
operational amplifier stage
OP2 can be used as a current or voltage source to supply external
components. OP2's positive input is connected internally to voltage
V
BG
so that the output current or output
voltage can be set across a wide range using one or two external resistors.
OPERATING AM460
General information on 2- and 3-wire applications and the use of the current output
In 3-wire operation (cf. Figure 3 right and Figure 7) the ground of the IC (pin
GND)
is connected up to the ex-
ternal 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.
2-wire system
signal source and
conditioning IC
GND
≠
Ground
V
CC
≠
V
S
GND
V
CC
I
OUT
R
L
V
S
3-wire system
signal source and
conditioning IC
GND
=
Ground
V
CC
=
V
S
I
OUT
R
L
V
CC
=
V
S
Ground
Ground
=
GND
Figure 3:
Difference between 2- and 3-wire operation
The construction of the V/I converter is such that output current
I
OUT
is largely independent of the current amplification
β
F
of external transistor
T
1
. Production-specific variations in the current amplification of the transistors used are compensated
for internally by the V/I converter.
2
analog microelectronics
April 2003
8/18
AME [ ANALOG MICROELECTRONICS ]
