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 13/21

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

Fax:

+49 (0)6131/91 073-30

Internet: http://www.analogmicro.de

Email: info@analogmicro.de

()

SET

IN

OUT

I

V

I

=

= 0

with

4

3

4

0

2

R

R

R

R

V

I

REF

SET

+

⋅

=

→

1

2

0

4

3

−

⋅

⋅

=

SET

REF

I

R

V

R

R

(9)

The output current range (e.g. 16mA) is set by the selection of external resistors R1 and R2 (or

fine adjustment with R0 ). Output current IOUT is then calculated as:

SET

VI

I

IN

OUT

I

R

G

G

V

I

+

⋅

=

0

with

GAIN

IA

I

G

G

G

⋅

=

and

0

=

ZA

V

(10)

If the offset of the AM452 signal source and input amplifier (IA) is such that it cannot be

ignored, when setting the output current range (gain)

(

)

0

=

IN

OUT V

I

also changes. This shift

must possibly be accounted for by making a fine adjustment to R3 and R4. If the offset of the

signal source and input amplifier is not relevant to the required degree of precision, Equations

(9) and (10) continue to apply.

OPERATING AM452: IMPORTANT POINTS TO NOTE

1. When using AM452 it is imperative that external capacitor C1 (a ceramic capacitor) is

always connected. Care must be taken that the value of the capacitor does not exceed the

range of values given in the boundary conditions – also within the temperature range (see

Table 2). In 2-wire operation ceramic capacitor C2 must also be used.

2. All AM452 function blocks not required by the application (OP2 or VREF) must be

placed in a defined (and allowed) operating state.

3. The voltages at the IA inputs (pins IN+ and IN-) must always lie within input voltage

range CMIR.

4. At the current output a load resistance of 600Ω maximum is permissible for 3-wire

operation.

5. The values of external resistors R0, R1, R2, R3, R4, R5, R6 and R7 must be selected within

the permissible range given in the boundary conditions.

6. The tolerances of the resistors and their temperature coefficients are entered into the

overall error.

7. In order to avoid temperature gradients it is imperative that the transistor is placed far

enough away from IC AM452 and that a sufficient temperature outlet is ensured.

8. In a 2-wire setup with a minimum output (offset) current of IOUT min the current balance

(the total domestic power supply across a temperature range of < IOUT min) of the IC and all

connected components (such as sensors) must be taken into account.