Industrial Converter and Protector IC

AM460

analog microelectronics

April 2003

8/18

reduce power dissipation the transistor is an external component and protected against reverse polarity by an

additional diode D1. Via pin SET an offset current ISET can be set at output IOUT (with the help of the inter-

nal voltage reference and an external voltage divider as shown in Figure 2, for example). External resistor R0

permits the output current to be finely adjusted with parallel operation of current and the voltage output. For

the output current provided by T1 the following ratio applies:

SET

INDAI

OUT

I

R

V

I

+

=

0

8

with

0

2R

V

I

SET

SET =

(3)

with VINDAI the voltage at INDAI and VSET the voltage at pin SET (V/I converter inputs, Figure 2)

2.

4. The AM460 reference voltage source enables voltage to be supplied to external components (such as sen-

sors, microprocessors, etc.). The reference voltage value VREF can be set via pin 13 VSET. If pin VSET is not

connected, VREF = 5V; if VSET is switched to ground, VREF = 10V. Values between these can be set if two

external resistors are used (inserted between pin VREF and pin VSET and between pin VSET and GND).

External (ceramic) capacitor C1 at pin VREF stabilises the reference voltage. It must be connected even if

the voltage reference is not in use.

5. The additional operational amplifier stage OP2 can be used as a current or voltage source to supply external

components. OP2's positive input is connected internally to voltage VBG so that the output current or output

voltage can be set across a wide range using one or two external resistors.

OPERATING AM460

General information on 2- and 3-wire applications and the use of the current output

In 3-wire operation (cf. Figure 3 right and Figure 7) the ground of the IC (pin GND) is connected up to the ex-

ternal mass of the system Ground. The system's supply voltage VS is connected to pin VCC and pin VCC to pin

RS+.

In 2-wire operation (cf. Figure 3 left and Figure 7) system supply voltage VS is connected to pin RS+ and pin

VCC to RS-. The ground of the IC (pin GND) is connected to the node between resistor R5 and load resistor RL

(current output IOUT). IC ground (GND) is not the same as system ground (Ground)!! The output signal is picked

up via load resistor RL which connects current output IOUT to the system ground.

2 The construction of the V/I converter is such that output current I

OUT is largely independent of the current amplification βF

of external transistor T1. Production-specific variations in the current amplification of the transistors used are compensated

for internally by the V/I converter.

R

L

V

S

2-wire system

signal source and

conditioning IC

GND

Ground

≠

V

CC ≠ VS

Ground

R

L

3-wire system

signal source and

conditioning IC

GND

Ground

=

V

CC = VS

Ground

GND

=

GND

V

CC

I

OUT

I

OUT

VV

CC

S

=

Figure 3: Difference between 2- and 3-wire operation