REV. C

–10–

AD8519/AD8529

Slew rate related distortion would not be present at the lower

voltages because the AD8519 is so fast at 2.1 V/

ms. A general

rule of thumb for determining the necessary slew rate for an

audio system is to take the maximum output voltage range of

the device given the design’s power rails and divide by two.

In Figure 2, the power rails are 2.7 V and the output is rail-to-

rail. Enter these numbers into the equation: 2.7/2 is 1.35 V and

the minimum ideal slew rate is 1.35 V/

ms.

While this data sheet gives only one audio example, many audio

circuits are enhanced with the use of the AD8519. Following

are a few examples: active audio filters such as bass, treble, and

equalizers; PWM filters at the output of audio DACs; buffers and

summers for mixing stations; and gain stages for volume control.

1k

AD8519

2.7V

30.9k

2.7V

3.09k

C1

1 F

1nF

NPO

46.4k

93.1k

2.7V

MIC

IN

240pF

48k

CODEC LINE IN

OR MIC IN

10 F ELECT

Figure 2. 10

Microphone Preamplifier

Two-Element Varying Bridge Amplifier

There are a host of bridge configurations available to designers.

For a complete analysis, look at the ubiquitous bridge and its differ-

ent forms. Please refer to the 1992 Amplifier Applications Guide

*.

*Adolfo Garcia and James Wong, Chapter 2, 1992 Amplifier Applications Guide.

Figure 3 is a schematic of a two-element varying bridge. This con-

figuration is commonly found in pressure and flow transducers.

With two-elements varying, the signal will be 2

¥ as compared to

a single-element varying bridge. The advantages of this type of

bridge are gain setting range, no signal input equals 0 V out, and

single-supply application. Negative characteristics are nonlinear

operation and required R matching. Given these sets of conditions,

requirements, and characteristics, the AD8519 can be success-

fully used in this configuration because of its rail-to-rail output

and low offset. Perhaps the greatest benefits of the AD8519,

when used in the bridge configuration, are the advantages it can

bring when placed in a remote bridge sensor. For example, the

tiny SC70 and SOT-23 packages will reduce the overall sensor

size; low power allows for remote powering via batteries or solar

cells, high output current drive to drive a long cable, and 2.7 V

operation for two-cell operation.

R

R

R

R

AD8519

2.7V

Figure 3. Two-Element Varying Bridge Amplifier