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參數(shù)資料
| 型號： | LM4844 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Stereo 1.2W Audio Sub-system with 3D Enhancement |
| 中文描述： | 1.2W的立體聲音頻子系統(tǒng)三維增強系統(tǒng) |
| 文件頁數(shù)： | 17/21頁 |
| 文件大?。?/td> | 983K |
| 代理商： | LM4844 |
Application Information
(Continued)
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is
critical for low noise performance and high power supply
rejection. Applications that employ a 5V regulator typically
use a 10μF in parallel with a 0.1μF filter capacitors to stabi-
lize the regulator’s output, reduce noise on the supply line,
and improve the supply’s transient response. However, their
presence does not eliminate the need for a local 1.0μF
tantalum bypass capacitance connected between the
LM4844’s supply pins and ground. Keep the length of leads
and traces that connect capacitors between the LM4844’s
power supply pin and ground as short as possible.
SELECTING EXTERNAL COMPONENTS
Input Capacitor Value Selection
Amplifying the lowest audio frequencies requires a high
value input coupling capacitor (C
in Figure 1). In many
cases, however, the speakers used in portable systems,
whether internal or external, have little ability to reproduce
signals below 50Hz. Applications using speakers with this
limited frequency response reap little improvement; by using
a large input capacitor.
The internal input resistor (R
i
) and the input capacitor (C
i
)
produce a high pass filter cutoff frequency that is found using
Equation (13).
f
c
= 1 / (2
π
R
i
C
i
)
(11)
As an example when using a speaker with a low frequency
limit of 50Hz and R
i
= 20k
, C
, using Equation (13) is
0.19μF. The 0.22μF C
shown in Figure 4 allows the LM4844
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 pin. Since C
B
determines how fast
the LM4844 settles to quiescent operation, its value is critical
when minimizing turn-on pops. The slower the LM4844’s
outputs ramp to their quiescent DC voltage (nominally V
DD
/
2), the smaller the turn-on pop. Choosing C
equal to 2.2μF
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 10
times the value of C
. This ensures that output transients are
eliminated when the LM4844 transitions in and out of shut-
down mode. Connecting a 2.2μF capacitor, C
, between the
BYPASS pin and ground improves the internal bias voltage’s
stability and improves the amplifier’s PSRR. The PSRR im-
provements increase as the bypass pin capacitor value in-
creases. However, increasing the value of C
will increase
wake-up time. The selection of bypass capacitor value, C
B
,
depends on desired PSRR requirements, click and pop per-
formance, wake-up time, system cost, and size constraints.
L
www.national.com
17
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| LM4850 | Mono 1.5 W / Stereo 300 mW Power Amplifier |
| LM4850LD | Mono 1.5 W / Stereo 300 mW Power Amplifier |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM4844_07 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Stereo 1.2W Audio Sub-System with 3D Enhancement |
| LM4844TL/NOPB | 功能描述:接口—CODEC RoHS:否 制造商:Texas Instruments 類型: 分辨率: 轉(zhuǎn)換速率:48 kSPs 接口類型:I2C ADC 數(shù)量:2 DAC 數(shù)量:4 工作電源電壓:1.8 V, 2.1 V, 2.3 V to 5.5 V 最大工作溫度:+ 85 C 安裝風格:SMD/SMT 封裝 / 箱體:DSBGA-81 封裝:Reel |
| LM4844TLEVAL | 功能描述:BOARD EVALUATION LM4844TL RoHS:否 類別:編程器，開發(fā)系統(tǒng) >> 評估板 - 音頻放大器 系列:Boomer® 產(chǎn)品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:1 系列:- |
| LM4844TLX/NOPB | 功能描述:接口—CODEC RoHS:否 制造商:Texas Instruments 類型: 分辨率: 轉(zhuǎn)換速率:48 kSPs 接口類型:I2C ADC 數(shù)量:2 DAC 數(shù)量:4 工作電源電壓:1.8 V, 2.1 V, 2.3 V to 5.5 V 最大工作溫度:+ 85 C 安裝風格:SMD/SMT 封裝 / 箱體:DSBGA-81 封裝:Reel |
| LM4845 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Output Capacitor-less Audio Subsystem with Programmable National 3D |
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