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 R1/R2, using equation 2, becomes

()

R

R

V

RI

I

INmax

OUTmax

SET

1

2

0

2

1

=

−

−

The current ISET is used to set the output current offset and can be calculated by using equation 3

()

()

IV

V

R

RR

R

RR

R

SET

IN

REF

SET

SET

==

⋅

+−

++

0

2

0

43

34

()

With R3 = R4 the set resistor RSET becomes (equation 4)

R

RR I

V

SET

SET

REF

≈

4

04

Example 1: Output current range 4...20mA

In this case the values of the external devices (V

IN = 05

K V, VREF = 5V ) are as follows

R0 = 25

Ω

R3 = R4 = 33k

Ω

RSET

≈ 2.64kΩ

R5 = 40

Ω

R1/R2

≈ 5.25

RL = 0...500

Ω

C1 = 2.2

µF

Example 2: Output current range 0...20mA

In this case the values of the external devices (V

IN = 010

K V, VREF = 5V ) are as follows

R0 = 25

Ω

R3 = R4 = 33k

Ω

RSET = 0

Ω

R5 = 40

Ω

R1/R2

≈ 9

RL = 0...500

Ω

C1 = 2.2

µF

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

VREF

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