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參數(shù)資料
| 型號： | LM4849 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Stereo 2W Audio Power Amplifiers with DC Volume Control and Input Mux |
| 中文描述： | 立體聲2W的音頻功率放大器直流音量控制和輸入復(fù)用器 |
| 文件頁數(shù)： | 15/19頁 |
| 文件大?。?/td> | 690K |
| 代理商： | LM4849 |
Application Information
(Continued)
(7)
As an example when using a speaker with a low frequency
limit of 150Hz, the input coupling capacitor using Equation
(7), is 0.063μF. The 0.33μF input coupling capacitor shown
in
Figure 1
allows the LM4849 to drive high efficiency, full
range speaker whose response extends below 30Hz.
OPTIMIZING CLICK AND POP REDUCTION
PERFORMANCE
The LM4849 contains circuitry that minimizes turn-on and
shutdown transients or “clicks and pops”. For this discus-
sion, turn-on refers to either applying the power supply volt-
age or when the shutdown mode is deactivated. While the
power supply is ramping to its final value, the LM4849’s
internal amplifiers are configured as unity gain buffers. An
internal current source changes the voltage of the BYPASS
pin in a controlled, linear manner. Ideally, the input and
outputs track the voltage applied to the BYPASS pin. The
gain of the internal amplifiers remains unity until the voltage
on the bypass pin reaches 1/2 V
. As soon as the voltage
on the bypass pin is stable, the device becomes fully opera-
tional. Although the BYPASS pin current cannot be modified,
changing the size of C
alters the device’s turn-on time
and the magnitude of “clicks and pops”. Increasing the value
of C
reduces the magnitude of turn-on pops. However,
this presents a tradeoff: as the size of C
increases, the
turn-on time increases. There is a linear relationship be-
tween the size of C
and the turn-on time. Here are
some typical turn-on times for various values of C
Bypass
:
C
Bypass
T
ON
0.01μF
0.1μF
0.22μF
0.47μF
1.0μF
2ms
20ms
44ms
94ms
200ms
RIGHT AND LEFT LINE OUT
Applications such as notebook computers can take advan-
tage of a line output signal to connect to external devices
such as monitors or audio/visual equipment that sends or
receives line level signals. The LM4849 has two outputs
which connect to the outputs of the internal input amplifiers
that drive the volume control inputs. These input amplifiers
can drive loads of
>
1k
(such as powered speakers) with a
rail-to-rail signal. Since the output signal present on the
RIGHT Line Out and LEFT Line Out pins is biased to V
DD
/2,
coupling capacitors need to be connected in series with the
load. Typical values for the coupling capacitors are 0.33μF to
1.0μF. If polarized coupling capacitors are used, connect
their "+" terminals to the respective output pin.
Since the Line Out outputs precede the internal volume
control, the signal amplitude will be equal to the input sig-
nal’s magnitude and cannot be adjusted. However, the input
amplifier’s closed-loop gain can be adjusted using external
resistors. These 20K resistors are shown in Figure 1 (R1 -
R8 ) and they set each input amplifier’s gain to -1. Use
Equation 8 to determine the input and feedback resistor
values for a desired gain.
- A
v
= R
2
/ R
3
(8)
Adjusting the input amplifier’s gain sets the minimum gain for
that channel. Although the single ended outputs of the
Bridge Output Amplifiers can be used to drive line level
outputs, it is recommended that the Right & Left Line Out-
puts simpler signal path be used for better performance.
STEREO-INPUT MULTIPLEXER (STEREO MUX)
The LM4849 has two stereo inputs. The MUX CONTROL pin
controls which stereo input is active.Applying 0V to the MUX
CONTROL pin selects stereo input 1. Applying V
DD
to the
MUX CONTROL pin selects stereo input 2.
MICRO-POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the
LM4849’s shutdown function. Activate micro-power shut-
down by applying V
to the SHUTDOWN pin. When active,
the LM4849’s micro-power shutdown feature turns off the
amplifier’s bias circuitry, reducing the supply current. The
logic threshold is typically V
DD
/2. The low 0.7 μA typical
shutdown current is achieved by applying a voltage that is as
near as V
DD
as possible, to the SHUTDOWN pin. A voltage
that is less than V
DD
may increase the shutdown current.
The Logic Level Truth Table shows the logic signal levels
that activate and deactivate micro-power shutdown and
headphone amplifier operation.
There are a few ways to control the micro-power shutdown.
These include using a single-pole, single-throw switch, a
microprocessor, or a microcontroller. When using a switch,
connect an external 10k
pull-up resistor between the
SHUTDOWN pin and V
. Connect the switch between the
SHUTDOWN pin and ground. Select normal amplifier opera-
tion by closing the switch. Opening the switch connects the
SHUTDOWN pin to V
through the pull-up resistor, activat-
ing micro-power shutdown. The switch and resistor guaran-
tee that the SHUTDOWN pin will not float. This prevents
unwanted state changes. In a system with a microprocessor
or a microcontroller, use a digital output to apply the control
voltage to the SHUTDOWN pin. Driving the SHUTDOWN pin
with active circuitry eliminates the need for a pull up resistor.
L
www.national.com
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PDF描述 |
|---|---|
| LM4849MH | Stereo 2W Audio Power Amplifiers with DC Volume Control and Input Mux |
| LM4852 | Integrated Audio Amplifier System |
| LM4852LQ | Integrated Audio Amplifier System |
| LM4852ITL | Integrated Audio Amplifier System |
| LM4854IBL | 1.9W Monaural, 85mW Stereo Headphone Audio Amplifier |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM4849MH | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Stereo 2W Audio Power Amplifiers with DC Volume Control and Input Mux |
| LM4849MH/NOPB | 功能描述:IC AMP AUDIO PWR 2.2W AB 28TSSOP RoHS:是 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:Boomer® 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:2,500 系列:DirectDrive® 類型:H 類 輸出類型:耳機(jī)，2-通道（立體聲） 在某負(fù)載時最大輸出功率 x 通道數(shù)量:35mW x 2 @ 16 歐姆 電源電壓:1.62 V ~ 1.98 V 特點(diǎn):I²C，麥克風(fēng)，靜音，短路保護(hù)，音量控制 安裝類型:表面貼裝 供應(yīng)商設(shè)備封裝:25-WLP（2.09x2.09） 封裝/外殼:25-WFBGA，WLCSP 包裝:帶卷 (TR) |
| LM4849MHX/NOPB | 功能描述:IC AMP AUDIO PWR 2.2W AB 28TSSOP RoHS:是 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:Boomer® 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:2,500 系列:DirectDrive® 類型:H 類 輸出類型:耳機(jī)，2-通道（立體聲） 在某負(fù)載時最大輸出功率 x 通道數(shù)量:35mW x 2 @ 16 歐姆 電源電壓:1.62 V ~ 1.98 V 特點(diǎn):I²C，麥克風(fēng)，靜音，短路保護(hù)，音量控制 安裝類型:表面貼裝 供應(yīng)商設(shè)備封裝:25-WLP（2.09x2.09） 封裝/外殼:25-WFBGA，WLCSP 包裝:帶卷 (TR) |
| LM4850 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Mono 1.5 W / Stereo 300 mW Power Amplifier |
| LM4850A E WAF | 制造商:Texas Instruments 功能描述: |
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