Industrial V/I Converter and Protector IC

AM462

analog microelectronics

December2006

Analog Microelectronics GmbH

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

15/20

An der Fahrt 13, D – 55124 Mainz

Fax:

+49 (0)6131/91 073 – 30

Rev. 2.4

Internet: http://www.analogmicro.de

Email:

info@analogmicro.de

Application for an input signal with an offset

It is not uncommon for input signals to have an offset (e.g. of 0.5...4.5V or 1...6V). For signals such

dimensioned as described in the following.

According to Equation 2 the following applies for a required current swing at the output of

0

6

8R

V

I

PIN

OUT

∆

=

∆

⇒

OUT

PIN

I

R

V

∆

=

∆

0

6

8

(10)

For an input current swing of

IN

PIN

V

V

G

∆

∆

=

6

(11)

If G < 1, the input signal can be routed directly to pin 6 (INDAI) via a voltage divider without OP1

having to be used (see Figure 9). With this circuitry the following results:

9

8

9

6

R

R

R

V

V

G

IN

PIN

+

=

∆

∆

=

⇒

1

6

9

8

−

∆

∆

=

PIN

IN

V

V

R

R

(12)

()

0

9

8

9

min

min

8

1

R

R

R

R

V

V

I

IN

IN

OUT

⋅

+

⋅

=

(13)

SET

IN

OUT

I

R

R

R

R

V

I

+

⋅

+

⋅

=

0

9

8

9

8

1

with

4

3

4

0

2

R

R

R

R

V

I

REF

SET

+

⋅

=

(14)

Example : 4..20mA Voltage-To-Current Transmitter with Input Signal Offset

that the output current has a range of 4...20mA. The circuitry is shown in Figure 9. OP1 is not used

here. It is, however, available to the user as an additional OP and can be used as an impedance

converter at the voltage-to-current converter input INDAI, for example.

V

456

.

3

mA

16

27

8

8

0

6

=

⋅

Ω

⋅

=

∆

=

∆

OUT

PIN

I

R

V

Using Equation 12 the following applies:

157

.

0

V

456

.

3

V

456

.

3

V

4

6

6

9

8

≈

−

=

∆

∆

−

∆

=

PIN

PIN

IN

V

V

V

R

R

⇒

8

9

35

.

6

R

R

⋅

=