AM452 – Voltage-to-current transducer IC

with a differential input

Analog Microelectronics GmbH

An der Fahrt 13, D – 55124 Mainz

February 2008 - Rev 1.2 - Page 17/21

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

Fax:

+49 (0)6131/91 073-30

Internet: http://www.analogmicro.de

Email: info@analogmicro.de

Typical 2-wire application with a differential input signal

2) Example 2: VIN = 0...100mV differential, IOUT = 4...20mA (2-wire)

In order to determine the system resistors R0 to R5 must first be determined.

For a measuring bridge with a signal of VIN = 0...100mV (without an offset) at the IA input

the external components in the AM452 circuitry should be dimensioned in such a way that the

output current range is 4...20mA. AM452 is configured in such a way that the entire current,

including the chip's quiescent current, flows through R0 (example for the 2-wire application).

As in Example 1, R2 and R4 can be freely selected within the boundary conditions. In this

example a value of 10kΩ has been chosen for R2, with 5kΩ selected for R4. VREF = 5V. The

value of R0 has been set to 33kΩ. Applying Equations (12) and (13) the values for R1 and R3

are as follows:

(

)

)

5

(

5

33

2

5

33

8

)

10

1

(

5

1

.

0

(

02

.

0

3

1

Ω

+

Ω

⋅

Ω

⋅

+

Ω

⋅

Ω

+

⋅

⋅

=

k

R

k

k

R

V

A

)

5

(

5

33

2

5

004

.

0

3

Ω

+

Ω

⋅

Ω

⋅

=

k

R

k

A

Ground

V

S

I

OUT

R

1

R

2

R

3

R

4

C

1

R

0

T

1

D

1

R

5

R

L

R

SET

C

2

GND

V

BG

IA

14

13

11

16

9

Voltage Reference

1

OP1

3

4

2

AM452

OP2

5

12

8

10

15

G

VI

7

G

SET SET Stage

ZERO Stage

}

V/I Converter

IC ground: GND

System ground: Ground

different

potentials!

2-wire

connection

Figure 7: Typical 2-wire application for differential input signals