LM4900 National Semiconductor, LM4900 Datasheet - Page 15

• Manufacturer Part Number: LM4900
• Description: 265mW at 3.3V Supply Audio Power Amplifier with Shutdown Mode
• Manufacturer: National Semiconductor

Application Information
From Equation 5, the minimum A
Since the desired input impedance was 20 k , and with a
A
R
bandwidth requirements which must be stated as a pair of
−3 dB frequency points. Five times away from a pole gives
0.17 dB down from passband response which is better than
the required
As stated in the External Components section, R
junction with C
The high frequency pole is determined by the product of the
desired high frequency pole, f
A
25MHz. This figure displays that if a designer has a need to
design an amplifier with a higher differential gain, the
LM4900 can still be used without running into bandwidth
problems.
= 100kHz which is much smaller than the LM4900 GBWP of
VD
VD
i
= R
. With a A
of 2, a ratio of 1:1 of R
C
i
F
= 20 k . The final design step is to address the
1/(2
±
VD
0.25 dB specified.
*
i
20 k
create a highpass filter.
f
= 2 and f
H
R
f
= 20kHz x 5 = 100kHz
L
F
= 100Hz/5 = 20Hz
*
/R
20 Hz) = 0.397µF; use 0.39µF
i
= A
H
F
= 100kHz, the resulting GBWP
VD
to R
/2
H
, and the differential gain,
VD
i
results in an allocation of
is 1.55; use A
(6)
(Continued)
VD
i
in con-
= 2.
(5)
15
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