Industrial Converter and Protector IC
cuit in Figure 5 the following applies:
I
S
=
V
BG
1 . 27 V
=
R
SET
R
SET
AM460
(12)
The bridge symbol represents the component to be supplied with current (e.g. a piezoresistive sensing element
or temperature sensor).
Example 1:
A supply current of
I
S
= 1mA is to be set. Using Equation 12 the following value is calculated for external re-
sistor
R
SET
, which in turn stipulates the size of the current:
R
SET
=
V
BG
1 . 27 V
=
=
1 . 27 k
Ω
1mA
I
S
Connecting OP2 as a voltage reference
In addition to the integrated voltage reference OP2 can also be used to supply voltage to external components
such as A/D converters and microprocessors, for example. Lower voltages can be generated (e.g. 3.3V) which
with the increasing miniaturisation of devices and need for ever lower levels of power dissipation in digital
components is today of growing importance.
The additional operational amplifier OP2 can easily be connected up as a voltage reference. Using the circuit in
R
V
CVREF
=
V
BG
1
+
6
=
1 . 27 V
R
7
R
1
+
6
R
7
(13)
Example 2:
A voltage of
V
CVREF
= 3.3V is to be set. Using Equation 13 the following ratio is calculated for external resistors
V
CVREF
OP2 connected as voltage
reference
1
µP
R
6
2
R
7
AM460
OP2
V
BG
Figure 6:
Connecting up a voltage reference
analog microelectronics
April 2003
11/18
AME [ ANALOG MICROELECTRONICS ]
