AM452 – Voltage-to-current transducer IC

with a differential input

Analog Microelectronics GmbH

An der Fahrt 13, D – 55124 Mainz

February 2008 - Rev 1.2 - Page 19/21

Phone: +49 (0)6131/91 073-0

Fax:

+49 (0)6131/91 073-30

Internet: http://www.analogmicro.de

Email: info@analogmicro.de

Using OP2 as a current source

The additional operational amplifier OP2 can easily be configured as a constant current

source. Using the circuitry shown in Figure 8 the following equation is generated:

S

S

BG

S

R

R

V

I

V

27

.

1

=

=

(14)

The bridge symbol is supposed to represent the component to be supplied with current (such

as a piezoresistive sensing element or a temperature sensor, for example).

Example

: A supply current of IS = 1mA is to be set. Using Equation (14) the below value is

accrued for external resistor RS, which determines the quantity of current:

Ω

=

=

=

k

27

.

1

mA

1

V

27

.

1

S

BG

S

I

V

R

Using OP2 as a voltage source

In addition to the integrated voltage reference OP2 can also be used to supply voltage to

external components such as A/D converters or microprocessors, for example. This permits

lower supply voltages of 3.3V, for example, to be generated. The following is derived from

the circuitry in Figure 9:













+

=













+

=

7

6

7

6

1

V

27

.

1

1

R

R

R

R

V

V

BG

CVREF

(15)

Example

:

A voltage of VCVREF = 3.3V is to be set. Using Equation (15) the following ratio is

provided for external resistors R6 and R7:

6

.

1

1

6

.

2

1

7

6

=

−

≈

−

=

BG

CVREF

V

V

R

R

Example values of R7 = 10kΩ and R6 = 16kΩ are accrued for the resistors.