VOLTAGE/CURRENT CONVERTER

AM422

analog microelectronics

April 99

6/10

the input voltage VIN has to change to

∆∆

VV

R

RR

PIN

IN

4

2

12

=

+













(8)

With the value of the relationship of the resistors R1 and R2

R

R

VV

V

IN

PIN

PIN

1

2

4

4

=

−

∆∆

∆

(9)

the additional offset current can be calculated as

II

I

I

V

R

R

RR

SET

OUTmin

INmin

OUTmin

INmin

=−

=−

+













2

0

2

12

(10)

The value of the set resistor can then be found using equation 4

In respect to the load resistor RL, the value of the supply voltage VS has to be considered with care.

The following relation is generally valid (see equation 1):

VI

R

V

S

OUTmax

L

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).

V

S [V]

R

L [Ω]

6

35

V

CCmin

= 6V

R

Lmax

= 500

Ω

I

OUTmax = 20mA

16

R

VV

I

L

SCCmin

OUTmax

≤

−

24

12

500

Operating Area

0

300

0

Figure 4