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 15/21

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

Fax:

+49 (0)6131/91 073-30

Internet: http://www.analogmicro.de

Email: info@analogmicro.de

Due to the algorithm upon which it is based the program also accounts for the spec. tolerances

of the IC and the components connected to it.

APPLICATIONS

Typical 3-wire application with a differential input signal

The aim of the calculation is the dimensioning of resistors R0 to R5.

In 3-wire operation (see Figure 6) the IC's connection to ground (pin 14 or GND) is connected

to the system ground (Ground) which is applied externally. System supply voltage VS is

connected to pin 10 or VCC and pin VCC to pin 11 or RS+. In this configuration AM452's

quiescent current does then not flow via resistor R0.

Figure 6 depicts the 3-wire application in which the differential output signal of a measuring

bridge supplied with current is amplified and converted. Power is supplied to the measuring

bridge by operational amplifier OP2 (c.f.: Using OP2 as a current source).

It is assumed in this application that no negative differential input voltages occur. Pin 13 (ZA)

is thus connected to the IC ground GND.

According to Equations (9) and (10) the following applies to output current IOUT:

SET

I

IN

OUT

I

R

G

V

I

+

=

0

8

mit

0

=

ZA

V

(11)

mit













+

=

=

2

1

1

5

R

R

G

G

G

GAIN

IA

I

und

4

3

4

0

2

R

R

R

R

V

I

REF

SET

+

⋅

=

(12)

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

GND

V

BG

IA

14

13

11

16

9

Voltage Reference

1

OP1

3

4

2

AM452

OP2

5

12

8

10

15

V/I Converter

G

VI

7

3-wire-connection

G

SET

SET Stage

ZERO Stage

Figure 6: 3-wire application for differential input signals

Figure 6 illustrates a

typical 3-wire circuit

with a positive,

differential input

signal which can be

used for calibrated

sensing elements, for

example. The offset

current is set using the

SET stage and the full

scale via the gain at

OP1.