UNIVERSAL AMPLIFIER IC

AM400

analog microelectronics

October 2005

Analog Microelectronics GmbH

Phone:

+49 (0)6131/91 073 – 0

13/21

An der Fahrt 13, D – 55124 Mainz

Fax:

+49 (0)6131/91 073 – 30

Rev.: 4.2

Internet: http://www.analogmicro.de

Email:

info@analogmicro.de

APPLICATIONS

1) Typical 3-wire application with a differential input signal

In 3-wire operation (cf. Figure 5, for example) the IC ground (pin GND) is connected up to the

and pin VCC to pin RS+.

Figure 5 shows a 3-wire application in which the differential output signal of a current-powered

measuring bridge is amplified and converted. Operational amplifier OP3 supplies the measuring

SET

SET

BG

S

R

R

V

I

V

27

.

1

=

=

(13)

For the above application it is assumed that no negative input voltages are present. Pin ZA is first

connected to the IC’s ground GND. According to Equation 3 the following then applies to output

IN

V

OUT

V

G

V

=

with

2

.

2

1

5

2











+

=

=

R

R

G

G

G

G

OP

GAIN

IA

V

(14)

Ground

V

S

I

OUT

R

1

R

2

R

IAL

R

3

R

4

C

1

R

0

T

1

D

1

R

5

R

L

R

SET

3-wire connection

Load resistor to minimize the offset

voltage at the IAoutput.

Negative offset voltages can be

compensated for using pin ZA.

If the pin is not in use it must be

connected to IC ground GND.

V

BG

17

5

IA

7

6

10

18

15

14

13

12

11

20

V

I

16

19

Voltage reference

1

9

OP1

8

3

4

2

AM400-0

OP2

OP3

V

OUT

Figure 5:

Typical 3-wire application for differential input