VOLTAGE/CURRENT CONVERTER

AM422

analog microelectronics

April 99

10/10

TYPICAL TWO–WIRE APPLICATION (0 – 1V)

Used in a two–wire circuit (AM422–2) ground pin 7 (GND,

⊥) is connected between R5 and the

load resistor (Figure 9). The relationship R1/R2, using equation 2, becomes

()

R

R

V

RI

I

INmax

OUTmax

SET

1

2

0

2

1

=

−

−

The current ISET is used to set the output current offset and can be calculated by using equation 3

()

()

IV

V

R

RR

R

RR

R

SET

IN

REF

SET

SET

==

⋅

+−

++

0

2

0

43

34

()

With R3 = R4 the set resistor RSET becomes (equation 4)

R

RR I

V

SET

SET

REF

≈

4

04

Example 4: Output current range 4...20mA

In this case the values of the external devices (VIN = 0...1V) are as follows

R0 = 25

Ω

R3 = R4 = 33k

Ω

RSET

≈ 2.64kΩ

R5 = 40

Ω

R1/R2

≈ 0.25

RL = 0...500

Ω

C1 = 2.2

µF

C2 = 100nF

C

1

R

4

R

3

V

REF

R

0

V

S

I

OUT

R

L

Ground

3

4

7

G = 1

Amplifier

2

1

VREF

2

V

IN

8

V

SET

V

OFFSET

R

1

R

2

R

SET

5

V

I

6

5/10 V Reference

AM422

−2

R

5

D

1

T

1

C

2

Figure 9

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for the use of this information, and all use of such information shall be entirely at the user's own risk. Prices and specifications are subject to change without notice. No patent rights or licences to any of

the circuits described herein are implied or granted to any third party. Analog Microelectronics does not authorise or warrant any Analog Microelectronics product use in life support devices and/or

systems.