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參數資料
| 型號： | LM4845ITL |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | Output Capacitor-less Audio Subsystem with Programmable National 3D |
| 中文描述： | 0.5 W, 2 CHANNEL, AUDIO AMPLIFIER, PBGA25 |
| 封裝： | MICRO, SMD-25 |
| 文件頁數： | 26/29頁 |
| 文件大小： | 1392K |
| 代理商： | LM4845ITL |
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Application Information
(Continued)
increase as the bypass pin capacitor value increases. Too
large, however, increases turn-on time and can compromise
the amplifier’s click and pop performance. The selection of
bypass capacitor values, especially C
B
, depends on desired
PSRR requirements, click and pop performance (as ex-
plained in the section, Proper Selection of External Compo-
nents), system cost, and size constraints.
SELECTING EXTERNAL COMPONENTS
Input Capacitor Value Selection
Amplifying the lowest audio frequencies requires high value
input coupling capacitor (C
in Figures 1 & 2). A high value
capacitor can be expensive and may compromise space
efficiency in portable designs. In many cases, however, the
speakers used in portable systems, whether internal or ex-
ternal, have little ability to reproduce signals below 150Hz.
Applications using speakers with this limited frequency re-
sponse reap little improvement by using large input capaci-
tor.
The internal input resistor (R
), nominal 20k
, and the input
capacitor (C
) produce a high pass filter cutoff frequency that
is found using Equation (15).
f
c
= 1 / (2
π
R
i
C
i
)
(15)
As an example when using a speaker with a low frequency
limit of 150Hz, C
i
, using Equation (15) is 0.053μF. The
0.22μF C
shown in
Figure 1
allows the LM4845 to drive high
efficiency, full range speaker whose response extends below
40Hz.
Bypass Capacitor Value Selection
Besides minimizing the input capacitor size, careful consid-
eration should be paid to value of C
B
, the capacitor con-
nected to the BYPASS bump. Since C
B
determines how fast
the LM4845 settles to quiescent operation, its value is critical
when minimizing turn-on pops. The slower the LM4845’s
outputs ramp to their quiescent DC voltage (nominally V
/
2), the smaller the turn-on pop. Choosing C
equal to 1.0μF
along with a small value of C
(in the range of 0.1μF to
0.39μF), produces a click-less and pop-less shutdown func-
tion. As discussed above, choosing C
no larger than neces-
sary for the desired bandwidth helps minimize clicks and
pops. C
’s value should be in the range of 5 times to 7 times
the value of C
. This ensures that output transients are
eliminated when power is first applied or the LM4845 re-
sumes operation after shutdown.
L
www.national.com
26
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相關代理商/技術參數 |
參數描述 |
|---|---|
| LM4845ITL/NOPB | 功能描述:音頻放大器 RoHS:否 制造商:STMicroelectronics 產品:General Purpose Audio Amplifiers 輸出類型:Digital 輸出功率: THD + 噪聲: 工作電源電壓:3.3 V 電源電流: 最大功率耗散: 最大工作溫度: 安裝風格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| LM4845ITLX/NOPB | 功能描述:音頻放大器 RoHS:否 制造商:STMicroelectronics 產品:General Purpose Audio Amplifiers 輸出類型:Digital 輸出功率: THD + 噪聲: 工作電源電壓:3.3 V 電源電流: 最大功率耗散: 最大工作溫度: 安裝風格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| LM4846 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Output Capacitor-less Audio Subsystem with Programmable National 3D |
| LM4846TL | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Output Capacitor-less Audio Subsystem with Programmable National 3D |
| LM4846TL/NOPB | 功能描述:音頻放大器 RoHS:否 制造商:STMicroelectronics 產品:General Purpose Audio Amplifiers 輸出類型:Digital 輸出功率: THD + 噪聲: 工作電源電壓:3.3 V 電源電流: 最大功率耗散: 最大工作溫度: 安裝風格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
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