參數(shù)資料
型號(hào): LM4849MH
廠商: NATIONAL SEMICONDUCTOR CORP
元件分類(lèi): 音頻控制
英文描述: Stereo 2W Audio Power Amplifiers with DC Volume Control and Input Mux
中文描述: 2 CHANNEL(S), VOLUME CONTROL CIRCUIT, PDSO28
封裝: TSSOP-28
文件頁(yè)數(shù): 18/19頁(yè)
文件大?。?/td> 690K
代理商: LM4849MH
Application Information
(Continued)
supply voltage must also not create a situation that violates
of maximum power dissipation as explained above in the
Power Dissipation
section.
After satisfying the LM4849’s power dissipation require-
ments, the minimum differential gain needed to achieve 1W
dissipation in an 8
load is found using Equation (13).
(11)
Thus, a minimum overall gain of 2.83 allows the LM4849’s to
reach full output swing and maintain low noise and THD+N
performance.
The last step in this design example is setting the amplifier’s
3dB frequency bandwidth. To achieve the desired
±
0.25dB
pass band magnitude variation limit, the low frequency re-
sponse must extend to at least one-fifth the lower bandwidth
limit and the high frequency response must extend to at least
five times the upper bandwidth limit. The gain variation for
both response limits is 0.17dB, well within the
±
0.25dB
desired limit. The results are an
f
L
= 100Hz/5 = 20Hz
(12)
and an
f
H
= 20kHz x 5 = 100kHz
(13)
As mentioned in the
Selecting Proper External Compo-
nents
section, R
i
(Right & Left) and C
i
(Right & Left) create
a highpass filter that sets the amplifier’s lower bandpass
frequency limit. Find the coupling capacitor’s value using
Equation (17).
C
i
1/(2
π
R
i
f
L
)
(14)
The result is
1/(2
π
*20k
*20Hz) = 0.397μF
(15)
Use a 0.39μF capacitor, the closest standard value.
The product of the desired high frequency cutoff (100kHz in
this example) and the differential gain A
VD
, determines the
upper passband response limit. With A
= 3 and f
=
100kHz, the closed-loop gain bandwidth product (GBWP) is
300kHz. This is less than the LM4849’s 3.5MHz GBWP. With
this margin, the amplifier can be used in designs that require
more differential gain while avoiding performance,restricting
bandwidth limitations.
L
www.national.com
18
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