Industrial Converter and Protector IC

AM460

analog microelectronics

April 2003

11/18

cuit in Figure 5 the following applies:

SET

SET

BG

S

R

R

V

I

V

27

.

1

=

=

(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 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:

Ω

=

=

=

k

27

.

1

mA

1

V

27

.

1

S

BG

SET

I

V

R

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:













+

=













+

=

7

6

7

6

1

V

27

.

1

1

R

R

R

R

V

V

BG

CVREF

(13)

Example 2:

A voltage of VCVREF = 3.3V is to be set. Using Equation 13 the following ratio is calculated for external resistors

V

BG

AM460

OP2

1

OP2 connected as voltage

reference

2

V

CVREF

R

6

R

7

µP

Figure 6: Connecting up a voltage reference