LM4872IBP datasheet(10/14 Pages) NSC

10 / 14 page

Application Information (Continued)

HIGHER GAIN AUDIO AMPLIFIER

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 R

3 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 R

3 =

20k

Ω and C

4 = 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.

DS101230-24

Figure 2

LM4872IBP Datasheet(PDF) 10 Page - National Semiconductor (TI)