Industrial V/I Converter and Protector IC

AM462

Analog Microelectronics GmbH

An der Fahrt 13, D – 55124 Mainz

Oktober 2007 – Rev.2.5 -Page 14/20

Phone: +49 (0)6131/91 073-0

Fax: +49 (0)6131/91 073-30

Internet:

http://www.analogmicro.de

Email: info@analogmicro.de

Example : 4…20mA Voltage-To-Current Converter in 2-wire application

To convert a signal of VINP = 0...1V at the OP1 input the external components are to be dimensioned

in such a way that the output current has a range of 4...20mA. The following applies:

mA

4

8

8

0

0

+

⋅

=

+

⋅

=

R

G

V

I

R

G

V

I

GAIN

INP

SET

GAIN

INP

OUT

With R0 = 27Ω and ISET = 4mA. Equation(4) produces the following relation between resistor R3

and R4:

15

.

22

1

mA

4

27

2

V

5

1

2

0

4

3

≈

−

⋅

Ω

⋅

=

−

=

SET

REF

I

R

V

R

R

and thus the following value for the gain:

456

.

3

V

1

mA

16

27

8

8

max

0

=

⋅

Ω

⋅

=

−

=

INP

SET

OUT

GAIN

V

I

I

R

G

⇒

456

.

2

1

456

.

3

2

1

=

−

=

R

R

Observing the given boundary conditions, the following values are obtained for the external

components:

R1 ≈ 24.56kΩ

R2 = 10kΩ

R3 ≈ 44.3kΩ

R4 = 2kΩ

R0 = 27Ω

R5 = 39Ω

RL = 0...600Ω

C1 = 2.2µF

C2 = 100nF

Ground

T

1

D

1

R

5

R

L

1

Single-ended

input voltage

Connections setting unused function blocks to a defined operating point

1

2

AM462

OP2

R

1

R

2

4

OP1

5

3

R

3

C

1

R

0

14

6

13

15

16

IC ground: GND

System ground: Ground

}different

potentials!

GND

2-wire

connection

C

2

8

9

11

10

V

R

4

I

Voltage Reference

V

INP

V

S

I

OUT

V

BG

Figure 8:

Typical 2-wire operation for input signals referenced to ground