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參數(shù)資料
| 型號： | LM4866MTE |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 2.2W Stereo Audio Amplifier |
| 中文描述： | 3.2 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO20 |
| 封裝： | 6.50 X 4.40 MM, 0.90 MM HEIGHT, EXPOSED PAD, TSSOP-20 |
| 文件頁數(shù)： | 14/21頁 |
| 文件大?。?/td> | 644K |
| 代理商： | LM4866MTE |
Application Information
(Continued)
AUDIO POWER AMPLIFIER DESIGN
Audio Amplifier Design: Driving 1W into an 8
Load
The following are the desired operational parameters:
Power Output:
Load Impedance:
Input Level:
Input Impedance:
Bandwidth:
1W
RMS
8
1V
RMS
20k
100Hz20 kHz
±
0.25 dB
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 Supply Voltage curve in the
Typical Performance Char-
acteristics
section. Another way, using Equation (4), is to
calculate the peak output voltage necessary to achieve the
desired output power for a given load impedance. To ac-
count for the amplifier’s dropout voltage, two additional volt-
ages, based on the Dropout Voltage vs Supply Voltage in the
Typical Performance Characteristics
curves, must be
added to the result obtained by Equation (8). The result in
Equation (9).
(8)
V
DD
≥
(V
OUTPEAK
+ (V
OD
TOP
+ V
OD
BOT
))
(9)
The Output Power vs Supply Voltage graph for an 8
load
indicates a minimum supply voltage of 4.6V. This is easily
met by the commonly used 5V supply voltage. The additional
voltage creates the benefit of headroom, allowing the
LM4866 to produce peak output power in excess of 1W
without clipping or other audible distortion. The choice of
supply voltage must also not create a situation that violates
maximum power dissipation as explained above in the
Power Dissipation
section.
After satisfying the LM4866’s power dissipation require-
ments, the minimum differential gain is found using Equation
(10).
(10)
Thus, a minimum gain of 2.83 allows the LM4866’s to reach
full output swing and maintain low noise and THD+N perfor-
mance. For this example, let A
VD
= 3.
The amplifier’s overall gain is set using the input (R
i
) and
feedback (R
) resistors. With the desired input impedance
set at 20k
, the feedback resistor is found using Equation
(11).
R
f
/R
i
= A
VD
/2
(11)
The value of R
f
is 30k
.
The last step in this design example is setting the amplifier’s
3dB frequency bandwidth. To achieve the desired
±
0.25dB
pass band magnitude variation limit, the low frequency re-
sponse must extend to at least onefifth the lower bandwidth
limit and the high frequency response must extend to at least
five times the upper bandwidth limit. The gain variation for
both response limits is 0.17dB, well within the
±
0.25dB
desired limit. The results are an
f
L
= 100Hz/5 = 20Hz
(12)
and an
F
H
= 20kHzx5 = 100kHz
(13)
As mentioned in the
External Components
section, R
i
and C
i
create a highpass filter that sets the amplifier’s lower
bandpass frequency limit. Find the coupling capacitor’s
value using Equation (14).
(14)
the result is
1/(2
π
*
20k
*
20Hz) = 0.398μF
(15)
Use a 0.39μF capacitor, the closest standard value.
The product of the desired high frequency cutoff (100kHz in
this example) and the differential gain, A
VD
, determines the
upper passband response limit. With A
= 3 and f
=
100kHz, the closed-loop gain bandwidth product (GBWP) is
300kHz. This is less than the LM4866’s 3.5MHz GBWP. With
this margin, the amplifier can be used in designs that require
more differential gain while avoiding performance-lrestricting
bandwidth limitations.
RECOMMENDED PRINTED CIRCUIT BOARD LAYOUT
Figures 2 through 6 show the recommended four-layer PC
board layout that is optimized for the 24-pin LQ-packaged
LM4866 and associated external components. Figures 7
through 11 show the recommended four-layer PC board
layout that is optimized for the 20-pin MTE-packaged
LM4866 and associated components. Figures 12 through 14
show the recommended two-layer PC board layout that is
optimized for the 20-pin MT-packaged LM4866 and associ-
ated components. These circuits are designed for use with
an external 5V supply and 3
(or greater) speakers for the
LQ- and MTE-packaged LM4866 and 4
(or greater) speak-
ers for the MT-packaged LM4866.
This circuit board is easy to use. Apply 5V and ground to the
board’s V
and GND pads, respectively. Connect speakers
between the board’s -OUTA and +OUTA and OUTB and
+OUTB pads. Apply the stereo input signal to the input pins
labeled ’-INA’ and ’-INB.’ The stereo input signal’s ground
references are connected to the respective input channel’s
’GND’ pin, adjacent to the input pins.
L
www.national.com
14
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM4866MTE/NOPB | 功能描述:音頻放大器 2.2W Stereo Audio Amp RoHS:否 制造商:STMicroelectronics 產(chǎn)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(fēng)格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| LM4866MTEX | 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 |
| LM4866MTEX/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 |
| LM4866MTEXNOPB | 制造商:National Semiconductor 功能描述:Audio Amp Speaker 2-CH Stereo 3.2W Class-AB 20-Pin HTSSOP EP T/R 制造商:National Semiconductor 功能描述:Audio Amp Speaker 2-CH Stereo 3.2W Class-AB 20-Pin TSSOP EP T/R |
| LM4867 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Output-Transient-Free Dual 2.1W Audop Amplifier Plus No Coupling Capacitor Stereo Headphone Function |
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