TS925 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
Manufacturer
TS925 Datasheet PDF : 17 Pages
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TS925
Using the TS925 as a preamplifier and speaker driver
3 Using the TS925 as a preamplifier and speaker
driver
The TS925 is an input/output rail-to-rail quad BiCMOS operational amplifier. It is able to operate
with low supply voltages (2.7V) and to drive low output loads such as 32Ω.
As an illustration of these features, the following technical note highlights many of the
advantages of the device in a global audio application.
3.1 Application circuit
Figure 16 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
reference level (VCC/2).
The power supply is delivered from two LR6 batteries (2 x 1.5V nominal).
Preamplifier
The operators A1 and A4 are wired with a non-inverting gain of respectively:
• A1# (R4/(R3+R17))
• A4# R6/R5
With the following values chosen:
• R4 = 22kΩ - R3 = 50Ω - R17 = 1.2kΩ
• R6 = 47kΩ - R5 = 1.2kΩ,
The gain of the preamplifier chain is therefore equal to 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, useful in many microphone preamplifier applications. The mean rectified peak level of
the output signal envelope is used to control the preamplifier gain.
11/17
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