CURRENT CONVERTER IC

AM402

analog microelectronics

April 99

4/8

FUNCTIONAL DIAGRAMS

FUNCTIONAL DESCRIPTION

AM402 is a monolithically integrated current converter which has been specially developed for the proc-

essing of differential bridge signals. By varying a few external components, the output current can be set to

various values within a wide range. Only an external output transistor T1 and a diode D1 are needed (See

Figure 7 and Figure 8) in addition to the resistors R0 – R5 and the capacitor C1 (C2). The external transistor

decreases the power dissipation of the IC and the diode protects the transistor against reverse polarity. The

maximum power dissipation of the components must be taken into consideration when selecting the transis-

tor and diode. Typical values for the external components are given in the following Description of Appli-

cations.

AM402 can principally be used in the implementation of two- and three-wire systems for industrial applica-

tions. A schematic diagram illustrates a three-wire system in Figure 2. Here, the differential input voltage

(VIN) is shown as a variable resistor. The external reference point Ground is identical to the ground of the IC

(GND) and the supply voltage of the IC matches that of the system: VCC = VS. In two-wire configurations,

however (Figure 3), the ground of the IC (GND) is connected between resistors R5 and RL. In this instance,

the supply voltage of the IC (VCC) is dependent on the supply voltage of the system (VS ) and the value of the

load resistor (RL). It can be calculated using the equation:

V

I

IA

3

−Wire System

Ground

V

S

I

OUT

R

L

V

IN

Reference Voltage

R

IN

R

A

R

B

Figure 2

V

I

IA

2

−Wire System

V

S

I

OUT

R

L

Reference Voltage

Ground

V

IN

R

IN

R

A

R

B

Figure 3