Industrial V/I Converter and Protector IC

AM462

Analog Microelectronics GmbH

An der Fahrt 13, D – 55124 Mainz

Oktober 2007 – Rev.2.5 -Page 8/20

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

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

Internet:

http://www.analogmicro.de

Email: info@analogmicro.de

INITIAL OPERATION OF AM462

General information on 2- and 3-wire applications and the use of current

In 3-wire operation (cf. Figure 3 right and Figure 7) the ground of the IC (pin GND) is connected up

to the external mass of the system Ground. The system's supply voltage VS is connected to pin VCC

and pin VCC to pin RS+.

In 2-wire operation (cf. Figure 3 left and Figure 7) system supply voltage VS is connected to pin

RS+ and pin VCC to 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 resistor RL which connects current output IOUT to

the system ground.

In 2-wire operation the IC ground is "virtual" (floating), as with a constant load resistance the

supply voltage of the device VCC changes according to the current. As a rule, the following equation

applies to 2-wire operation:

()

L

IN

OUT

S

CC

R

V

I

V

V

−

=

(3)

The reason for this is that in 2-wire operation the IC is connected in series to the actual load resistor

RL. This is illustrated in Figure 3.

In 3-wire operation VCC = VS, as the IC ground is connected to the ground of the system.

Setting the output current range

When using amplification stage OP1 together with the V/I converter for voltage-to-current

conversion the offset of the output current should first be compensated for by suitable selection of

resistors R3 and R4. To this end the OP1 input must be connected to ground (VINP = 0). With the

short circuit at the input and by connecting up V/I converter pin VSET as shown in Figure 2 the

values of the output current according to Equation 2 are as follows:

R

L

V

S

2-wire system

signal source and

conditioning IC

GND Ground

≠

V

CC ≠ VS

Ground

R

L

3-wire system

signal source and

conditioning IC

GND Ground

=

V

CC = VS

Ground GND

=

GND

V

CC

I

OUT

I

OUT

VV

CC

S

=

Figure 3: The difference between 2- and 3-wire operation