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 10/21

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

Fax:

+49 (0)6131/91 073-30

Internet: http://www.analogmicro.de

Email: info@analogmicro.de

OPERATING AM452

2- and 3-wire applications in general [2]

As AM452 can function in both 2- and 3-wire operation through external contacting, it is

important to first differentiate between the two versions of the circuit.

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

IC supply voltage VCC changes according to the current. The following equation can generally

be applied to 2-wire operation:

( )

L

IN

OUT

S

CC

R

V

I

V

V

−

=

(5)

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 a 2-wire system the power consumption of the overall system (AM452 plus all external

components including the signal source and adjusting resistors) may not be more than IOUTmin

(e.g. 4mA).

In 3-wire operation Equation (5) no longer applies as the IC ground is connected to the

ground of the system. In 3-wire operation the supply voltage can be expressed as:

VCC = VS

(6)

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 basic difference between a 2- and 3-wire circuit

NB: The difference between GND and Ground must be clearly acknowledged!