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参数资料
| 型号： | LM4839MT/NOPB |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 音频控制 |
| 英文描述： | 2 CHANNEL(S), TONE CONTROL CIRCUIT, PDSO28 |
| 封装： | TSSOP-28 |
| 文件页数： | 13/34页 |
| 文件大小： | 1104K |
| 代理商： | LM4839MT/NOPB |
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AUDIO POWER AMPLIFIER
DESIGN
Audio Amplifier Design: Driving 1W into an 8
Load
The following are the desired operational parameters:
Power Output:
1 W
RMS
Load Impedance:
8
Input Level:
1 V
RMS
Input Impedance:
20 k
Bandwidth:
100 Hz20 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 (11), 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 (11). The result is
Equation (12).
(10)
V
DD ≥ (VOUTPEAK+(VODTOP +VODBOT))
(11)
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
LM4839 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
of maximum power dissipation as explained above in the
Power Dissipation section.
After satisfying the LM4839’s power dissipation require-
ments, the minimum differential gain needed to achieve 1W
dissipation in an 8
load is found using Equation (13).
(12)
Thus, a minimum overall gain of 2.83 allows the LM4839’s to
reach full output swing and maintain low noise and THD+N
performance.
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 one-fifth 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
(13)
and an
f
H = 20kHz x 5 = 100kHz
(14)
As mentioned in the Selecting Proper External Compo-
nents section, R
i (Right & Left) and Ci (Right & Left) create
a highpass filter that sets the amplifier’s lower bandpass
frequency limit. Find the coupling capacitor’s value using
Equation (17).
C
i≥ 1/(2πR ifL)
(15)
The result is
1/(2
π*20k*20Hz) = 0.397F
(16)
Use a 0.39F 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
VD = 3 and fH =
100kHz, the closed-loop gain bandwidth product (GBWP) is
300kHz. This is less than the LM4839’s 3.5MHz GBWP. With
this margin, the amplifier can be used in designs that require
more differential gain while avoiding performance,restricting
bandwidth limitations.
RECOMMENDED PRINTED
CIRCUIT BOARD LAYOUT
Figures 4 through 8 show the recommended four-layer PC
board layout that is optimized for the 8-pin LQ-packaged
LM4839 and associated external components. This circuit is
designed for use with an external 5V supply and 4
speak-
ers.
This circuit board is easy to use. Apply 5V and ground to the
board’s V
DD
and GND pads, respectively. Connect 4
speakers between the board’s OUTA and +OUTA and
OUTB and +OUTB pads.
LM4839
www.national.com
20
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM4840 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:Stereo 2W Audio Power Amplifiers with Digital Volume Control and Input Mux |
| LM4840LQ | 制造商:Texas Instruments 功能描述:AMP AUDIO POWER DC VOLT LLP-28 |
| LM4840LQ/NOPB | 功能描述:IC AMP AUDIO PWR 2.2W STER 28LLP RoHS:是 类别:集成电路 (IC) >> 线性 - 音頻放大器 系列:Boomer® 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:DirectDrive® 类型:H 类 输出类型:耳机，2-通道（立体声） 在某负载时最大输出功率 x 通道数量:35mW x 2 @ 16 欧姆 电源电压:1.62 V ~ 1.98 V 特点:I²C，麦克风，静音，短路保护，音量控制 安装类型:表面贴装 供应商设备封装:25-WLP（2.09x2.09） 封装/外壳:25-WFBGA，WLCSP 包装:带卷 (TR) |
| LM4840MH | 制造商:Texas Instruments 功能描述:AMP AUDIO STEREO 2W SMD TSSOP28 |
| LM4840MH/NOPB | 功能描述:IC AMP AUDIO PWR 2.2W AB 28TSSOP RoHS:是 类别:集成电路 (IC) >> 线性 - 音頻放大器 系列:Boomer® 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:DirectDrive® 类型:H 类 输出类型:耳机，2-通道（立体声） 在某负载时最大输出功率 x 通道数量:35mW x 2 @ 16 欧姆 电源电压:1.62 V ~ 1.98 V 特点:I²C，麦克风，静音，短路保护，音量控制 安装类型:表面贴装 供应商设备封装:25-WLP（2.09x2.09） 封装/外壳:25-WFBGA，WLCSP 包装:带卷 (TR) |
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