Datasheet

VOLTAGE/CURRENT CONVERTER AM422
analog microelectronics
April 99
8/10
TYPICAL THREE–WIRE APPLICATION (0 – 5/10V)
Used in a three–wire circuit (AM422–1) ground pin 7 (GND) is connected to Ground (Figure 7).
The relationship of 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 1: Output current range 4...20mA
In this case the values of the external devices (V
IN
= 05K V, V
REF
= 5V ) are as follows
R
0
= 25Ω R
3
= R
4
= 33kΩ R
SET
≈ 2.64kΩ R
5
= 40Ω
R
1
/R
2
≈ 5.25 R
L
= 0...500Ω C
1
= 2.2µF
Example 2: Output current range 0...20mA
In this case the values of the external devices (V
IN
= 010K V, V
REF
= 5V ) are as follows
R
0
= 25Ω R
3
= R
4
= 33kΩ R
SET
= 0Ω R
5
= 40Ω
R
1
/R
2
≈ 9 R
L
= 0...500Ω C
1
= 2.2µF
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
−
1
R
5
D
1
T
1
Figure 7