Application Information (Continued)
HIGHER GAIN AUDIO AMPLIFIER
DS101230-24
Figure 2
The LM4872 is unity-gain stable and requires no external
components besides gain-setting resistors, an input coupling
capacitor, and proper supply bypassing in the typical appli-
cation. However, if a closed-loop differential gain of greater
than 10 is required, a feedback capacitor may be needed as
shown in Figure 2 to bandwidth limit the amplifier. This feed-
back capacitor creates a low pass filter that eliminates
possible high frequency oscillations. Care should be taken
when calculating the -3dB frequency in that an incorrect
combination of R3 and C4 will cause rolloff before 20kHz. A
typical combination of feedback resistor and capacitor that
will not produce audio band high frequency rolloff is R3
=
20kΩ and C4 = 25pf. These components result in a -3dB
point of approximately 320 kHz. It is not recommended that
the feedback resistor and capacitor be used to implement a
band limiting filter below 100kHZ.
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