Datasheet

LM4990
SNAS184E –DECEMBER 2002–REVISED MAY 2013 www.ti.com
Figure 41. HIGHER GAIN AUDIO AMPLIFIER
The LM4990 is unity-gain stable and requires no external components besides gain-setting resistors, an input
coupling capacitor, and proper supply bypassing in the typical application. However, if a closed-loop differential
gain of greater than 10 is required, a feedback capacitor (C4) may be needed as shown in Figure 2 to bandwidth
limit the amplifier. This feedback 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 R
3
and
C
4
will cause rolloff before 20kHz. A typical combination of feedback resistor and capacitor that will not produce
audio band high frequency rolloff is R
3
= 20kΩ and C
4
= 25pf. These components result in a -3dB point of
approximately 320kHz.
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