am422 AME, Inc., am422 Datasheet - Page 5

• Manufacturer Part Number: am422
• Description: Voltage/current Converter - Analog Microelectronics
• Manufacturer: AME, Inc.

VOLTAGE/CURRENT CONVERTER
has to be connected between the resistors R
on the voltage V
Basically the IC AM422 is composed of 3 functional sections as they shown in Figure 1:
1. An operational amplifier input which allows the adjustment of the output current range with the
2. A voltage controlled current output, with a wide current range is adjustable with external resis-
3. A programmable voltage reference (VSET = N.C. or VSET = GND) can be used as an excitation
The output current is based on two partial currents: an adjustable offset current and a current relying
on the input signal V
For the adjustment of the AM422 two cases have to be differentiated. For input voltage ranges
without an offset voltage (0...5V, 0...10V) the adjustment of the output current range is as follows:
The minimum output current has to be set with an input voltage V
becomes
With R
The output current range has to be set with the transfer function of the IC and can be calculated by
The relationship of R
The adjustment of the IC using an input offset voltage (for example 0.5...4.5V) can be described as
follows. For a desired change of the output current of ∆I
analog microelectronics
two external resistors R
the output current range can be set.
tors R
voltage and corresponds to a minimal output current. The output current I
external transistor T
for constant voltage sensors or as supply for other external devices.
3
= R
SET
, R
4
and simplifications the set resistor R
3
S
and R
V
∆I
∆
I
I
R
R
R
and the load resistor R
OUT
SET
CC
I
SET
1
2
OUT
OUT
=
IN
(
1
(
V
≈
/R
V
4
. The transfer function of the AM422 is then
2
1
V
. The resistors fix the output offset current, which depends on the reference
IN
=
=
SET
, driven by the output of the IC pin 3 (OUT).
4
2
R I
S
I
0
becomes
∆

=
R R I
OUTmax
,
(
1
0
V
2
V
V
0
I
and R
R
OUTmax
PIN
IN
)
REF
OUT
V
4
0
=
INmax
)
4
=
R
˜
SET
1
−
0
R
2
I
I
. With the variation of the resistors the input voltage range and
SET
⋅
L
−
SET



V
I
(
SET
SET
V
L
=
SET
and can be calculated:
)
V
−
2
−
INmax
5
)
V
R
1
and R
+
REF
2
0
⇒
I
IN




 =

SET
R
( )
L
V
1
. In this case the IC supply voltage V
IN
R
+
V
is
∆
2
R
REF
V
R
OUT
0
PIN
2



⋅
4
2
(
=
(
R
R
4
2
3
+
R
+
0
IN
R
R
∆
SET
= 0V. The output offset current
4
I
+
OUT
)
R
−
SET
R
3
)
OUT
is supplied by the
AM422
CC
depends
April 99
5/10
(1)
(2)
(3)
(4)
(5)
(6)
(7)