- 您現(xiàn)在的位置：買(mǎi)賣(mài)IC網(wǎng) > PDF目錄385487 > LM4951 (National Semiconductor Corporation) Wide Voltage Range 1.8 Watt Audio Amplifier PDF資料下載
參數(shù)資料
| 型號(hào)： | LM4951 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Wide Voltage Range 1.8 Watt Audio Amplifier |
| 中文描述： | 寬電壓范圍1.8瓦音頻功率放大器 |
| 文件頁(yè)數(shù)： | 12/18頁(yè) |
| 文件大?。?/td> | 1119K |
| 代理商： | LM4951 |
第1頁(yè)第2頁(yè)第3頁(yè)第4頁(yè)第5頁(yè)第6頁(yè)第7頁(yè)第8頁(yè)第9頁(yè)第10頁(yè)第11頁(yè)當(dāng)前第12頁(yè)第13頁(yè)第14頁(yè)第15頁(yè)第16頁(yè)第17頁(yè)第18頁(yè)
Application Information
(Continued)
lation. Keep the length of leads and traces that connect
capacitors between the LM4951’s power supply pin and
ground as short as possible. Connecting a larger capacitor,
C
BYPASS
, between the BYPASS pin and ground improves
the internal bias voltage’s stability and improves the amplifi-
er’s PSRR. The PSRR improvements increase as the by-
pass 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 capaci-
tor values, especially C
, depends on desired PSRR
requirements, click and pop performance (as explained in
the section,
SELECTING EXTERNAL COMPONENTS
),
system cost, and size constraints.
MICRO-POWER SHUTDOWN
The LM4951 features an active-low micro-power shutdown
mode. When active, the LM4951’s micro-power shutdown
feature turns off the amplifier’s bias circuitry, reducing the
supply current. The low 0.01μA typical shutdown current is
achieved by applying a voltage to the SHUTDOWN pin that
is as near to GND as possible. A voltage that is greater than
GND may increase the shutdown current.
There are a few methods to control the micro-power shut-
down. These include using a single-pole, single-throw switch
(SPST), a microprocessor, or a microcontroller. When using
a switch, connect the SPST switch between the shutdown
pin and V
DD
. Select normal amplifier operation by closing the
switch. Opening the switch applies GND to the SHUTDOWN
pin activating micro-power shutdwon.The switch and internal
pull-down resistor guarantee 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 active-state voltage to the SHUTDOWN
pin.
SELECTING EXTERNAL COMPONENTS
Input Capacitor Value Selection
Two quantities determine the value of the input coupling
capacitor: the lowest audio frequency that requires amplifi-
cation and desired output transient suppression.
As shown in Figure 1, the input resistor (R
) and the input
capacitor (C
) produce a high pass filter cutoff frequency that
is found using Equation (6).
f
c
= 1/2
π
R
i
C
i
As an example when using a speaker with a low frequency
limit of 50Hz, C
, using Equation (6) is 0.159μF. The 0.39μF
C
shown in Figure 1 allows the LM4951 to drive high
efficiency, full range speaker whose response extends below
30Hz.
(6)
OPTIMIZING CLICK AND POP REDUCTION
PERFORMANCE
The LM4951 contains circuitry that eliminates turn-on and
shutdown transients ("clicks and pops"). For this discussion,
turn-on refers to either applying the power supply voltage or
when the micro-power shutdown mode is deactivated.
As the V
/2 voltage present at the BYPASS pin ramps to its
final value, the LM4951’s internal amplifiers are configured
as unity gain buffers. An internal current source charges the
capacitor connected between the BYPASS pin and GND in a
controlled 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 V
/2. As soon as the
voltage on the bypass pin is stable, there is a delay to
prevent undesirable output transients (“click and pops”). Af-
ter this delay, the device becomes fully functional.
AUDIO POWER AMPLIFIER DESIGN
Audio Amplifier Design: Driving 1.8W into an 8
BTL
The following are the desired operational parameters:
Power Output
Load Impedance
Input Level
Input Impedance
Bandwidth
The design begins by specifying the minimum supply voltage
necessary to obtain the specified output power. One way to
find the minimum supply voltage is to use the
Output Power
vs Power Supply Voltage
curve in the
Typical Performance
Characteristics
section. Another way, using Equation (7), is
to calculate the peak output voltage necessary to achieve
the desired output power for a given load impedance. To
account for the amplifier’s dropout voltage, two additional
voltages, based on the
Clipping Dropout Voltage vs Power
Supply Voltage
in the
Typical Performance Characteris-
tics
curves, must be added to the result obtained by Equa-
tion (7). The result is Equation (8).
1.8W
RMS
8
0.3V
RMS
(max)
20k
50Hz–20kHz
±
0.25dB
(7)
V
DD
= V
OUTPEAK
+ V
ODTOP
+ V
ODBOT
(8)
The commonly used 7.5V supply voltage easily meets this.
The additional voltage creates the benefit of headroom,
allowing the LM4951 to produce peak output power in ex-
cess of 1.8W without clipping or other audible distortion. The
choice of 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
LM4951’s power dissipation requirements, the minimum dif-
ferential gain needed to achieve 1.8W dissipation in an 8
BTL load is found using Equation (9).
(9)
Thus, a minimum gain of 12.6 allows the LM4951’s to reach
full output swing and maintain low noise and THD+N perfor-
mance. For this example, let A
= 13. The amplifier’s
overall BTL gain is set using the input (R
) and feedback (R
f
)
resistors of the first amplifier in the series BTL configuration.
Additionaly,A
V-BTL
is twice the gain set by the first amplifier’s
R
i
and R
f
. With the desired input impedance set at 20k
, the
feedback resistor is found using Equation (10).
R
f
/
R
i
= A
V-BTL
/
2
(10)
The value of R
f
is 130k
(choose 191k
, the closest value).
The nominal output power is 1.8W.
L
www.national.com
12
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| LM4953 | Ground-Referenced, Ultra Low Noise, Ceramic Speaker Driver |
| LM4953SD | Ground-Referenced, Ultra Low Noise, Ceramic Speaker Driver |
| LM4980 | 2 Cell Battery, 1mA, 42mW Per Channel High Fidelity Stereo Headphone Audio Amplifier for MP3 players |
| LM4980SD | 2 Cell Battery, 1mA, 42mW Per Channel High Fidelity Stereo Headphone Audio Amplifier for MP3 players |
| LM4992SD | 420mW Stereo Cell Phone Audio Amplifier |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM4951A | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Wide Voltage Range 1.8 Watt Audio Amplifier With Short Circuit Protection |
| LM4951ASD | 功能描述:音頻放大器 RoHS:否 制造商:STMicroelectronics 產(chǎn)品:General Purpose Audio Amplifiers 輸出類(lèi)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(fēng)格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| LM4951ASD/NOPB | 功能描述:音頻放大器 RoHS:否 制造商:STMicroelectronics 產(chǎn)品:General Purpose Audio Amplifiers 輸出類(lèi)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(fēng)格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| LM4951ASDBD | 功能描述:BOARD EVALUATION FOR LM4951A RoHS:否 類(lèi)別:編程器，開(kāi)發(fā)系統(tǒng) >> 評(píng)估板 - 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:1 系列:- |
| LM4951ASDBD/NOPB | 功能描述:音頻 IC 開(kāi)發(fā)工具 LM4951ASD EVAL BOARD RoHS:否 制造商:Texas Instruments 產(chǎn)品:Evaluation Kits 類(lèi)型:Audio Amplifiers 工具用于評(píng)估:TAS5614L 工作電源電壓:12 V to 38 V |
發(fā)布緊急采購(gòu)，3分鐘左右您將得到回復(fù)。