Datasheet

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
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BOUNDARY CONDITIONS
Parameter Symbol Conditions Min. Typ. Max. Unit
Sense Resistor R
0
I
OUTFS
= 20mA 17 27 38 
R

c = 20mA/I
OUTFS
c ⋅ 17 c ⋅ 27 c ⋅ 38

Stabilization Resistor R
5
I
OUTFS
= 20mA 35 40 45 
R
5
c = 20mA/I
OUTFS
c ⋅ 35 c ⋅ 40 c ⋅ 45

Load Resistance R
L
Limitation only for 3-wire operation 0 600 
Sum Gain Resistors R
1
+ R
2
20 200 k
Sum Offset Resistors R
3
+ R
4
20 200 k
V
REF
Capacitance C
1
Ceramic 1.9 2.2 5.0
µF
Output Capacitance C
2
Only for 2-wire operation 90 100 250 nF
D
1
Breakdown Voltage V
BR
35 50 V
T
1
Forward Current Gain β
F
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
G
GAIN
can be set via external resistors R
1
and R
2
. Protective circuitry against overvoltage is
integrated into the chip, limiting the voltage to the set value of the reference voltage. Output
voltage V
OUTAD
at pin OUTAD is calculated as:
GAININPOUTAD
GVV
⋅
= with
2
1
1
R
R
G
GAIN
+= (1)
where V
INP
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 T
1
; this in turn supplies
the actual output current I
OUT
. To reduce power dissipation the transistor is an external
component and protected against reverse polarity by an additional diode D
1
. Via pin SET an
offset current I
SET
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 R
0
permits the
output current to be finely adjusted with parallel operation of current and the voltage output. For
the output current provided by T
1
the following ratio applies: