lm4891mm National Semiconductor Corporation, lm4891mm Datasheet - Page 11

• Manufacturer Part Number: lm4891mm
• Description: 1 Watt Audio Power Amplifier
• Manufacturer: National Semiconductor Corporation

Application Information
As stated in the External Components section, R
junction with C
The high frequency pole is determined by the product of the
desired frequency pole, f
The LM4891 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-
C
i
≥ 1/(2π*20 kΩ*20 Hz) = 0.397 µF; use 0.39 µF
i
create a highpass filter.
H
, and the differential gain, A
(Continued)
FIGURE 2. Higher Gain Audio Amplifier
i
in con-
VD
.
11
With a A
300 kHz which is much smaller than the LM4891 GBWP of
2.5 MHz. This figure displays that if a designer has a need to
design an amplifier with a higher differential gain, the
LM4891 can still be used without running into bandwidth
limitations.
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 320 kHz.
3
= 20kΩ and C
VD
= 3 and f
4
= 25pf. These components result in a
H
3
= 100 kHz, the resulting GBWP =
and C
20007424
4
will cause rolloff before
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