參數(shù)資料
型號: LM4900MMX/NOPB
廠商: NATIONAL SEMICONDUCTOR CORP
元件分類: 音頻/視頻放大
英文描述: 0.675 W, 1 CHANNEL, AUDIO AMPLIFIER, PDSO8
封裝: 0.118 INCH, PLASTIC, MSOP-8
文件頁數(shù): 7/19頁
文件大?。?/td> 772K
代理商: LM4900MMX/NOPB
Application Information (Continued)
(5)
R
F/Ri =AVD/2
(6)
From Equation 5, the minimum A
VD is 1.55; use AVD =2.
Since the desired input impedance was 20 k
, and with a
A
VD of 2, a ratio of 1:1 of RF to Ri results in an allocation of
R
i =RF =20 k. The final design step is to address the
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 ±0.25 dB specified.
f
L = 100Hz/5 = 20Hz
f
H = 20kHz x 5 = 100kHz
As stated in the External Components section, R
i in con-
junction with C
i create a highpass filter.
C
i ≥ 1/(2π*20 k*20 Hz) = 0.397F;
use 0.39F
The high frequency pole is determined by the product of the
desired high frequency pole, f
H, and the differential gain,
A
VD. With a AVD = 2 and fH = 100kHz, the resulting GBWP
= 100kHz which is much smaller than the LM4900 GBWP of
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.
LM4900
www.national.com
15
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