Industrial V/I Converter and Protector IC

AM462

Analog Microelectronics GmbH

An der Fahrt 13, D – 55124 Mainz

Oktober 2007 – Rev.2.5 -Page 6/20

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

Fax: +49 (0)6131/91 073-30

Internet:

http://www.analogmicro.de

Email: info@analogmicro.de

BOUNDARY CONDITIONS

Parameter

Symbol

Conditions

Min.

Typ.

Max.

Unit

Sense Resistor

R0

IOUTFS = 20mA

17

27

38

R

c = 20mA/IOUTFS

c

⋅ 17

c

⋅ 27

c

⋅ 38

Stabilization Resistor

R5

IOUTFS = 20mA

35

40

45

R5

c = 20mA/IOUTFS

c

⋅ 35

c

⋅ 40

c

⋅ 45

Load Resistance

RL

Limitation only for 3-wire operation

0

600

Sum Gain Resistors

R1 + R2

20

200

k

Sum Offset Resistors

R3 + R4

20

200

k

VREF Capacitance

C1

Ceramic

1.9

2.2

5.0

µF

Output Capacitance

C2

Only for 2-wire operation

90

100

250

nF

D1 Breakdown Voltage

VBR

35

50

V

T1 Forward Current Gain

βF

BCX54/55/56, for example

50

150

DETAILED DESCRIPTION OF FUNCTIONS

AM462 is a modular, universal V/I converter and protector IC which has been specially developed

for the conditioning of voltage signals referenced to ground. It is designed for both 2- and 3-wire

operation in industrial applications (cf. application in Figure 8). AM462’s various functions are

depicted in the block diagram (Figure 2) which also illustrates how few external components are

required for the operation of this particular device.

AM462 consists of several modular function blocks (operational amplifiers, voltage-to-current

converters and references) which, depending on external configurations, can either be switched to

one another or operated separately (see the basic circuitry in Figure 2):

1. Operational amplifier stage OP1 enables a positive voltage signal to be amplified. OP1 gain

GGAIN can be set via external resistors R1 and R2. Protective circuitry against overvoltage is

integrated into the chip, limiting the voltage to the set value of the reference voltage. Output

voltage VOUTAD at pin OUTAD is calculated as:

GAIN

INP

OUTAD

G

V

V

⋅

=

with

2

1

1

R

R

G

GAIN

+

=

(1)

where VINP is the voltage at OP1’s input pin 6 (INP).

2. The internal voltage-to-current converter (V/I converter) provides a voltage-controlled current

signal at IC output IOUT (pin 8) which activates an external transistor T1; this in turn supplies

the actual output current IOUT. To 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 internal 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: