lm4990mm National Semiconductor Corporation, lm4990mm Datasheet - Page 15

• Manufacturer Part Number: lm4990mm
• Description: 2 Watt Audio Power Amplifier With Selectable Shutdown Logic Level
• Manufacturer: National Semiconductor Corporation

Application Information
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 appli-
cation. 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 elimi-
FIGURE 2. HIGHER GAIN AUDIO AMPLIFIER
(Continued)
15
nates possible high frequency oscillations. Care should be
taken when calculating the -3dB frequency in that an incor-
rect combination of R
20kHz. A typical combination of feedback resistor and ca-
pacitor that will not produce audio band high frequency rolloff
is R
-3dB point of approximately 320kHz.
3
= 20kΩ and C
4
= 25pf. These components result in a
3
and C
4
will cause rolloff before
20051024
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