Datasheet

LM4890
SNAS138L –SEPTEMBER 2001–REVISED MAY 2013 www.ti.com
The high frequency pole is determined by the product of the desired frequency pole, f
H
, and the differential gain,
A
VD
. With a A
VD
= 3 and f
H
= 100kHz, the resulting GBWP = 300kHz which is much smaller than the LM4890
GBWP of 2.5MHz. This calculation shows that if a designer has a need to design an amplifier with a higher
differential gain, the LM4890 can still be used without running into bandwidth limitations.
Figure 68. HIGHER GAIN AUDIO AMPLIFIER
The LM4890 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 68 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 320 kHz.
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