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 9/21

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

Fax:

+49 (0)6131/91 073-30

Internet: http://www.analogmicro.de

Email: info@analogmicro.de

SET stage

The SET stage permits the adjustment of the offset output current IOUTmin > 0mA. Together

with the V/I converter it effects the output current IOUT. Via pin 16 (SET) an offset current

ISET can be set at pin 8 (IOUT) e.g. with the help of the internal voltage reference and an

external voltage divider as shown in Figure 2, for example.

Voltage-to-current converter (V/I converter)

The voltage-to-current converter (V/I converter) compares the voltage drop across the

external sensing resistor R0 with a value of VSET GSET + VOP GVI and uses the result to

regulate transistor T1. It generates a suitable signal at the IC output pin 8 (IOUT) which

activates external transistor T1. This in turn supplies an output current of IOUT and accepts

the power dissipation of the output stage.

External resistor R0 permits the output current to be finely adjusted. For the output current

IOUT amplified by T1 the following ratio applies:

SET

VI

OP

OUT

I

R

G

V

I

+

⋅

=

0

=

SET

OP

I

R

V

+

0

8

with

0

R

G

V

I

SET

SET

SET

⋅

=

=

0

2R

V

SET

(3)/(4)

where VOP is the input voltage of the V/I converter and VSET the voltage at pin 16 (SET).

Reference voltage source

The reference voltage source (bandgap voltage source) enables voltage to be supplied to

external components (such as sensors, microprocessors, etc.). The reference voltage value

VREF can be set using pin 12 (VSET). If pin 12 is not connected, VREF = 5V; if pin 12 is

switched to ground, VREF = 10V. Values between these can be set if two external resistors

are used (inserted between pin 15 (VREF) and pin 12 (VSET) and between pin 12 (VSET)

and GND).

External capacitor C1 stabilizes the reference voltage. It must be connected even if the voltage

reference is not in use. It may not undershoot the given minimum value.

Additional operational amplifier OP2

The additional operational amplifier OP2 can be used as a current or voltage source to

supply external components. OP2's positive input must be connected internally to bandgap

voltage VBG so that the OP2 output voltage at pin 1 or CVREF can be set across a wide

range using external resistors.

The individual modules are described separately in the specifications. The reference voltage

source and the operational amplifier OP2 can be operated as independent circuit elements or

modules. Instrumentation amplifier IA, operational amplifier OP1 and the V/I converter form

a unit within the circuit and have the task of converting the voltage input signal into the

required output current.