VOLTAGE/CURRENT CONVERTER
TYPICAL TWO–WIRE APPLICATION (0 – 1V)
R
3
V
REF
6
8
AM422
C
1
R
SET
5
AM422−2
V
SET
V
REF
2
V
S
R
4
G
=1
V
OFFSET
5/10 V Reference
1
R
0
C
2
V
V
IN
4
2
Amplifier
R
1
R
2
7
I
3
T
1
D
1
R
5
I
OUT
R
L
Ground
Figure 9
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
1
V
INmax
=
−
1
R
2
2
R
0
(
I
OUTmax
−
I
SET
)
The current
I
SET
is used to set the output current offset and can be calculated by using equation 3
I
SET
(
V
IN
=
0
)
=
V
REF
(
R
4
+
R
SET
)
−
R
3
⋅
R
0
2
(
R
3
+
R
4
+
R
SET
)
With
R
3
=
R
4
the set resistor
R
SET
becomes (equation 4)
R
SET
≈
4
R
0
R
4
I
SET
V
REF
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
The information provided herein is believed to be reliable; however, Analog Microelectronics assumes no responsibility for inaccuracies or omissions. Analog Microelectronics assumes no responsibility
for the use of this information, and all use of such information shall be entirely at the user's own risk. Prices and specifications are subject to change without notice. No patent rights or licences to any of
the circuits described herein are implied or granted to any third party. Analog Microelectronics does not authorise or warrant any Analog Microelectronics product use in life support devices and/or
systems.
analog microelectronics
April 99
10/10
AME [ ANALOG MICROELECTRONICS ]
