Industrial Converter and Protector IC
AM460
cuit in Figure 5 the following applies:
VBG
1.27V
(12)
IS
=
=
RSET
RSET
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 IS = 1mA is to be set. Using Equation 12 the following value is calculated for external re-
sistor RSET, which in turn stipulates the size of the current:
VBG
IS
1.27V
1mA
RSET
=
=
= 1.27kΩ
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
Figure 6 the following applies:
R6
R7
R6
R7
(13)
VCVREF = VBG 1+
= 1.27 V 1 +
Example 2:
A voltage of VCVREF = 3.3V is to be set. Using Equation 13 the following ratio is calculated for external resistors
OP2 connected as voltage
reference
VCVREF
1
AM460
R6
R7
µP
2
OP2
VBG
Figure 6: Connecting up a voltage reference
analog microelectronics
April 2003
11/18
AME [ ANALOG MICROELECTRONICS ]
