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 14/21

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

Fax:

+49 (0)6131/91 073-30

Internet: http://www.analogmicro.de

Email: info@analogmicro.de

9. For applications where IOUT min > 0mA (e.g. 4mA) in both 2- and 3-wire applications the

following condition applies to the IA input values:

min

max

.

.

OUT

OUT

IA

OS

IA

FS

I

I

V

V

≥

,

where VFS.IA is the maximum input signal and VOS.IA the

positive offset at the input IA.

10. If signal source and/or input amplifier IA have a negative offset this can be compensated

for using corrective voltage VZA and a suitable voltage divider (R6 and R7; see Figure 2).

DIMENSIONING

Two possible dimensioning methods are suggested here.

Dimensioning the external components according to the equations given in the data

sheet

Dimensioning according to the equations given in the data sheet enables all modules to be

used, making it possible for the setup to be adapted to suit the most diverse application

requirements.

As a rule the offset of the AM452 input signal must be taken into account. If an input signal

offset is present and an offset current of IOUT min > 0mA is required, the following boundary

condition then applies:

min

max

.

.

OUT

OUT

IA

OS

IA

FS

I

I

V

V

≥

, where VFS.IA is the maximum input signal and

VOS.IA the positive offset at the input IA (see: chapter before). Should the signal source have a

negative offset, the offset can be set via pin 13 (ZA) and voltage divider R6 and R7 (see Figure

2). Equation (1) forms the basis for all other equations in this particular case.

If the offset is negligible, Equations (9) and (10) apply. See the following applications for

further details.

Dimensioning AM452's external components using an Excel spreadsheet

AM452's external components can also be dimensioned with the help of Excel spreadsheet

Kali_AM452.xls when the input signal is positive (see [3]). The algorithm is such that the

offset output current of 4mA can only be set via pin 13 (ZA) of the zero adjust stage. The SET

stage is not active. The full-scale output current is set to 20mA using the OP1 gain setting.

The calibration process is also based on the condition that the output signal should be a

4...20mA current loop signal in 2-wire operation.