VOLTAGE/CURRENT CONVERTER
the input voltage
V
IN
has to change to
R
2
∆
V
PIN
4
= ∆
V
IN
R
1
+
R
2
With the value of the relationship of the resistors
R
1
and
R
2
R
1
∆
V
IN
− ∆
V
PIN
4
=
R
2
∆
V
PIN
4
the additional offset current can be calculated as
I
SET
=
I
OUTmin
−
I
INmin
=
I
OUTmin
−
V
INmin
R
2
2
R
0
R
1
+
R
2
AM422
(8)
(9)
(10)
The value of the set resistor can then be found using equation 4
In respect to the load resistor
R
L
, the value of the supply voltage
V
S
has to be considered with care.
The following relation is generally valid (see equation 1):
V
S
≥
I
OUTmax
R
L
+
V
CCmin
.
(11)
The resulting operating range is indicated in Figure 4. Sample calculations and typical values for the
external components are listed in the
Application Notes
(beginning page 8).
R
L
[Ω]
R
L
≤
V
S
−
V
CCmin
I
OUTmax
V
CCmin
=
6V
R
Lmax
=
500Ω
I
OUTmax
= 20mA
500
300
Operating Area
0
0
6
12
16
24
35
V
S
[V]
Figure 4
analog microelectronics
April 99
6/10
AME [ ANALOG MICROELECTRONICS ]
