am422 AME, Inc., am422 Datasheet - Page 9

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

VOLTAGE/CURRENT CONVERTER
TYPICAL THREE–WIRE APPLICATION (0.5 – 4.5V)
Example 3: Output current range I
The transfer function of the output current I
For the 0.5 to 4.5V application (Figure 8) a change of the input voltage from ∆V
displayed over a change of the output current ∆I
With the voltage change at pin 4 (∆V
equation 8, becomes then
With that relation an offset current I
has to be adjusted (equation 10). With R
The values of the external devices than can be calculated as follows (V
R
R
C
analog microelectronics
Figure 8
0
1
1
/R
= 25Ω
= 2.2µF
2
≈ 4
R
V
SET
R
IN
4
R
1
R
2
V
I
I
R
∆
SET
OUT
SET
∆
SET
V
V
PIN
4
5
IN
=
AM4221
≈
=
4
V
I
R
R
I
4
OUTmin
REF
=
SET
3
1
2
R R I
= R
≈ 68kΩ
R
0
V
1
+
REF
R
+
4
4
2
I
−
R
= 33kΩ
IN
SET
2
I
Amplifier
G = 1
INmin
=
OUT
=
SET
I
800
SET
= 4...20mA, input voltage range V
4
=
from
PIN4
3
V
mV
+
I
= R
V
OUTmin
OFFSET
2
OUT
V
= 800mV, equation 7) the relationship of R
7
IN
R
4
R
3
0
the set resistor R
R
R
is (equation 2)
OUT



SET
2
− 2mA = 2mA
R
≈ 18kΩ
1
⇒
= 16mA.
R
≈ 1.32kΩ
V
+
5/10 V Reference
2
R
6
2



V
REF
R
R
1
2
SET
8
=
∆
can be calculated (equation 4)
I
V
C
IN
1
∆
REF
R
R
V
−
5
L
IN
PIN
= 40Ω
= 0...500Ω
∆
= 5V )
= 0.5...4.5V
V
1
2
3
4
PIN
4
=
IN
T
D
4
1
= 4V should be
R
1
AM422
0
R
1
5
/R
Ground
2
, using
April 99
R
I
OUT
V
L
S
9/10