VOLTAGE/CURRENT CONVERTER

AM422

analog microelectronics

April 99

4/10

FUNCTIONAL DIAGRAMS

FUNCTIONAL DESCRIPTION

The IC AM422 is an integrated voltage–to–current converter for a broad spectrum of possible single

ended input signals. With variations of a few external components the output current can be ad-

justed over a wide range. In addition to the resistors R0 – R5 and the capacitor C1 (C2), the circuitry

needs only an output transistor T1 and a diode D1. The external transistor decreases the power dissi-

pation of the IC and the diode is protecting the transistor against reverse polarity. Typical values for

the external components are listed in the Application Notes.

In principle the AM422 can be used as a two–wire or as a three–wire voltage–to–current interface.

The schematic of the entire system for the three–wire output is demonstrated on Figure 2. The ex-

ternal reference point Ground has to be identical to the ground pin 7 (GND) and the IC supply volt-

age becomes VCC = VS. Opposed to this, the ground pin 7 in the two–wire mode (Figure 3) (GND)

V

I

3

−Wire System

Ground

V

S

I

OUT

R

L

V

IN

Voltage Reference

Input

Amplifier

R

IN

R

A

Figure 2

V

I

2

−Wire System

Ground

V

S

I

OUT

R

L

Voltage Reference

Input

Amplifier

V

IN

R

IN

R

A

Figure 3