AM417 – Ratiometric instrumentation

amplifier with adjustable output stage

Analog Microelectronics GmbH

An der Fahrt 13, D – 55124 Mainz

July 2008 –Rev 3.1- Page 6/18

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

Fax: +49 (0)6131/91 073-30

Email: info@analogmicro.de

DESCRIPTION OF FUNCTIONS

AM417 is a ratiometric, adjustable interface IC which has been specially developed for the

conditioning of bridge signals for automotive applications. With its integrated, ratiometric current

source it is particularly suitable for the excitation of piezoresistive bridge devices in a constant

current mode. The IC enables simple calibration and temperature compensation of the input signals.

AM417 consist of three functional units:

Instrumentation amplifier

Using the input stage of the instrumentation amplifier (IA) the input signal is preamplified by

the output offset).

Current source

divider (10:1). With the OP acting as a ratiometric current source a resistor measuring cell can be

supplied with constant current within a range of 0.5 – 1.25mA.

1

10 R

V

I

VCC

(1)

Output stage

4

4

3

R

R

R

G

OUT

+

=

(2)

A current limitation has been integrated into the output stage. The limit circuit restricts output

( )

1

min

5

.

1

T

V

V

V

BE

VCC

VOUT

−

=

(3)

transistor emitter (see Figure 2). The current is thus calculated as:

()

2

2

1

max

mV

380

R

R

T

V

V

I

BE

THRESH

OUT

≈

−

=

(4)