參數(shù)資料
型號: LM4841MHX/NOPB
廠商: NATIONAL SEMICONDUCTOR CORP
元件分類: 音頻控制
英文描述: 2 CHANNEL(S), VOLUME CONTROL CIRCUIT, PDSO28
封裝: TSSOP-28
文件頁數(shù): 13/31頁
文件大?。?/td> 1138K
代理商: LM4841MHX/NOPB
Application Information (Continued)
At low, frequencies C
BA is a virtual open circuit and at high
frequencies, its nearly zero ohm impedance shorts R
BA. The
result is increased bridge-amplifier gain at low frequencies.
The combination of R
BA and CBA form a -6dB corner fre-
quency at
f
C = 1/(2
πR
BACBA)
(9)
The bridged-amplifier low frequency differential gain is:
A
VD = 2(RGFA +RBA)/RGIA
(10)
Using the component values shown in Figure 2 (R
GFA =
20k
,R
BA = 20k
, and C
BA = 0.068F), a first-order, -6dB
pole is created at 120Hz. Assuming R
GIA = 20k
, the low
frequency differential gain is 4. The input (C
in A and B) capaci-
tor values must be selected for a low frequency response
that covers the range of frequencies affected by the desired
bass-boost operation.
DC VOLUME CONTROL
The LM4841 has an internal stereo volume control whose
setting is a function of the DC voltage applied to the DC VOL
CONTROL pin.
The LM4841 volume control consists of 31 steps that are
individually selected by a variable DC voltage level on the
volume control pin. The range of the steps, controlled by the
DC voltage, are from 0dB - 78dB. Each gain step corre-
sponds to a specific input voltage range, as shown in table 2,
(on the following page.)
To minimize the effect of noise on the volume control pin,
which can affect the selected gain level, hysteresis has been
implemented. The amount of hysteresis corresponds to half
of the step width, as shown in Volume Control Characteriza-
tion Graph (DS200133-40).
For highest accuracy, the voltage shown in the ’recom-
mended voltage’ column of the table is used to select a
desired gain. This recommended voltage is exactly halfway
between the two nearest transitions to the next highest or
next lowest gain levels.
The gain levels are 1dB/step from 0dB to -6dB, 2dB/step
from -6dB to -36dB, 3dB/step from -36dB to -47dB, 4dB/step
from -47db to -51dB, 5dB/step from -51dB to -66dB, and
12dB to the last step at -78dB.
20028011
FIGURE 7. Low Frequency Enhancement ( MT/MH PINOUT )
LM4841
www.national.com
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相關(guān)PDF資料
PDF描述
LM4841MT/NOPB 2 CHANNEL(S), VOLUME CONTROL CIRCUIT, PDSO28
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LM4842MHX/NOPB 2 CHANNEL(S), TONE CONTROL CIRCUIT, PDSO28
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