LM4890MSLASHNOPB datasheet(22/36 Pages) TI

22 / 36 page

LM4890

SNAS138L – SEPTEMBER 2001 – REVISED MAY 2013

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The high frequency pole is determined by the product of the desired frequency pole, fH, and the differential gain,

AVD. With a AVD = 3 and fH = 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 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.

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LM4890M/NOPB Datasheet(PDF) 22 Page - Texas Instruments