VOLTAGE/CURRENT CONVERTER
FUNCTIONAL DIAGRAMS
Voltage Reference
R
A
AM422
3−Wire System
V
S
Input
Amplifier
V
IN
R
IN
V
I
OUT
I
R
L
Ground
Figure 2
Voltage Reference
R
A
2−Wire System
V
S
Input
Amplifier
V
IN
R
IN
V
I
OUT
I
R
L
Ground
Figure 3
FUNCTIONAL DESCRIPTION
The IC AM422 is an integrated voltage–to–current converter for a broad spectrum of possible single
ended input signals. With variations of a few external components the output current can be ad-
justed over a wide range. In addition to the resistors
R
0
–
R
5
and the capacitor
C
1
(C
2
), the circuitry
needs only an output transistor
T
1
and a diode
D
1
. The external transistor decreases the power dissi-
pation of the IC and the diode is protecting the transistor against reverse polarity. Typical values for
the external components are listed in the
Application Notes.
In principle the AM422 can be used as a two–wire or as a three–wire voltage–to–current interface.
The schematic of the entire system for the three–wire output is demonstrated on Figure 2. The ex-
ternal reference point
Ground
has to be identical to the ground pin 7 (GND) and the IC supply volt-
age becomes
V
CC
=
V
S
. Opposed to this, the ground pin 7 in the two–wire mode (Figure 3) (GND)
analog microelectronics
April 99
4/10
AME [ ANALOG MICROELECTRONICS ]
