Datasheet

Industrial Converter and Protector IC AM460
analog microelectronics
April 2003
8/18
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:
SET
INDAI
OUT
I
R
V
I
+=
0
8
with
0
2R
V
I
SET
SET
= (3)
with V
INDAI
the voltage at INDAI and V
SET
the voltage at pin SET (V/I converter inputs, Figure 2)
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
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.
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: Difference between 2- and 3-wire operation