Datasheet

VOLTAGE/CURRENT CONVERTER AM422
analog microelectronics
April 99
10/10
TYPICAL TWO–WIRE APPLICATION (0 – 1V)
Used in a two–wire circuit (AM422–2) ground pin 7 (GND, ⊥) is connected between R
5
and the
load resistor (Figure 9). The relationship R
1
/R
2
, using equation 2, becomes
()
R
R
V
RI I
INmax
OUTmax SET
1
2
0
2
1=
−
−
The current I
SET
is used to set the output current offset and can be calculated by using equation 3
()
()
IV
V
R
RR R
RRR
SET IN
REF SET
SET
== ⋅
+−
++
0
2
0
43
34
()
With R
3
= R
4
the set resistor R
SET
becomes (equation 4)
R
RRI
V
SET
SET
REF
≈
4
04
Example 4: Output current range 4...20mA
In this case the values of the external devices (V
IN
= 0...1V) are as follows
R
0
= 25Ω R
3
= R
4
= 33kΩ R
SET
≈ 2.64kΩ R
5
= 40Ω
R
1
/R
2
≈ 0.25 R
L
= 0...500Ω C
1
= 2.2µF C
2
= 100nF
C
1
R
4
R
3
V
REF
R
0
V
S
I
OUT
R
L
Ground
3
4
7
G = 1
Amplifier
2
1
V
REF
2
V
IN
8
V
SET
V
OFFSET
R
1
R
2
R
SET
5
V
I
6
5/10 V Reference
AM422
−
2
R
5
D
1
T
1
C
2
Figure 9
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