AM452 – Voltage-to-current transducer IC
with a differential input
SET stage
The SET stage permits the adjustment of the offset output current I
OUTmin
> 0mA. Together
with the V/I converter it effects the output current I
OUT
. Via pin 16 (SET) an offset current
I
SET
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 R
0
with a value of
V
SET
G
SET
+ V
OP
G
VI
and uses the result to
regulate transistor T
1
. It generates a suitable signal at the IC output pin 8 (IOUT) which
activates external transistor
T
1
. This in turn supplies an output current of
I
OUT
and accepts
the power dissipation of the output stage.
External resistor
R
0
permits the output current to be finely adjusted. For the output current
I
OUT
amplified by
T
1
the following ratio applies:
I
OUT
=
V
⋅
G
V
V
OP
⋅
G
VI
V
+
I
SET
=
OP
+
I
SET
with
I
SET
=
SET SET
=
SET
8
R
0
R
0
2R
0
R
0
(3)/(4)
where
V
OP
is the input voltage of the V/I converter and
V
SET
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
V
REF
can be set using pin 12 (VSET). If pin 12 is not connected,
V
REF
= 5V; if pin 12 is
switched to ground,
V
REF
= 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
C
1
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
V
BG
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.
Phone: +49 (0)6131/91 073-0
Fax:
+49 (0)6131/91 073-30
Internet:
http://www.analogmicro.de
Email: info@analogmicro.de
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
February 2008 - Rev 1.2 - Page 9/21
AME [ ANALOG MICROELECTRONICS ]
