AN1282 datasheet(1/2 Pages) STMICROELECTRONICS

Part #	AN1282

Description	PREAMPLIFIER AND SPEAKER DRIVER USING TS925

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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The TS925 is an input/output rail to rail quad BiC-

MOS operational amplifier. It is able to operate

with low supply voltages (2.7V) and to drive low

output loads such as 32

Ω.

As an illustration of these features, the following

technical note highlights many of the advantages

of the device in a global audio application.

APPLICATION CIRCUIT

Figure 1 shows two operators (A1, A4) used in a

preamplifier configuration, and the two others in a

push-pull configuration driving a headset.

The phantom ground is used as a common refer-

ence level (VCC/2).

The power supply is delivered from two LR6 bat-

ter-ies (2x1.5V nominal).

Preamplifier : the operators A1 and A4 are wired

with a non inverting gain of respectively :

u A1# (R4/(R3+R17))

u A4# R6/R5

With the following values chosen :

u R4=22k

Ω - R3=50Ω - R17=1.2kΩ

u R6=47k

Ω - R5=1.2kΩ,

the gain of the preamplifier chain is thus 58dB.

Alternatively, the gain of A1 can be adjusted by

choosing a JFET transistor Q1 instead of R17.

This JFET voltage controlled resistor arrangement

forms an automatic level control (ALC) circuit,

use-ful in many MIC preamplifier applications.

The mean rectified peak level of the output signal

envelope is used to control the preamplifier gain.

Figure 1 : Electrical Schematic

AN1282

APPLICATION NOTE

PREAMPLIFIER AND SPEAKER DRIVER USING TS925

June 2000

by F. MARICOURT

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