Industrial Converter and Protector IC

AM460

analog microelectronics

April 2003

14/18

Typical 2-wire application with an input signal referenced to ground

In 2-wire operation (cf. Figure 8) system supply voltage VS is connected up to pin RS+ and pin VCC to pin RS-.

The ground of the IC (pin GND) is connected to the node between resistor R5 and load resistor RL (current output

IOUT). IC ground (GND) is not the same as system ground (Ground)!! The output signal is picked up via load re-

sistor RL which connects current output IOUT to the system ground.

For output current IOUT the following applies according to Equation 3:

SET

I

INP

OUT

I

R

G

V

I

+

⋅

=

0

8

with

2

1

1

R

R

G

G

GAIN

I

+

=

=

and

4

3

4

0

2

R

R

R

R

V

I

REF

SET

+

⋅

=

Example 4:

To obtain 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.

mA

4

8

8

0

0

+

⋅

=

+

⋅

=

R

G

V

I

R

G

V

I

GAIN

INP

SET

I

INP

OUT

With R0 = 27Ω Equation 7 produces the following:

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 to be set:

Ground

T

1

D

1

R

5

R

L

1

Single-ended

input voltage

1

2

AM460

OP3

OP2

R

1

R

2

4

OP1

5

3

R

3

C

1

Voltage Reference

R

0

714

6

13

15

16

IC ground: GND

System ground: Ground

} Different

potentials!

GND

2-wire

connection

C

2

12

8

9

11

10

V

R

4

I

V

INP

V

S

I

OUT

V

BG

Connections setting unused function blocks to a defined operating point

Figure 8: Typical 2-wire application for input signals referenced to ground