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参数资料
| 型号： | LM3875MDC |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 音频／视频放大 |
| 英文描述： | 56 W, 1 CHANNEL, AUDIO AMPLIFIER, UUC |
| 封装： | DIE |
| 文件页数： | 6/21页 |
| 文件大小： | 582K |
| 代理商： | LM3875MDC |
Application Information (Continued)
voltage, usually about 15% higher. Supply voltage will also
rise 10% during high line conditions. Therefore, the maxi-
mum supply voltage is obtained from the following equation:
max. supplies
≈ ± (V
opeak + Vod(1 + regulation)(1.1) (7)
The input sensitivity and the output power specs determine
the minimum required gain as depicted below:
(8)
Normally the gain is set between 20 and 200; for a 40W, 8
audio amplifier this results in a sensitivity of 894 mV and
89 mV, respectively. Although higher gain amplifiers provide
greater output power and dynamic headroom capabilities,
there are certain shortcomings that go along with the so
called “gain”. The input referred noise floor is increased and
hence the SNR is worse. With the increase in gain, there is
also a reduction of the power bandwidth which results in a
decrease in feedback thus not allowing the amplifier to re-
spond as quickly to nonlinearities. This decreased ability to
respond to nonlinearities increases the THD + N specifica-
tion.
The desired input impedance is set by R
IN. Very high values
can cause board layout problems and DC offsets at the out-
put. The value for the feedback resistance, R
f1, should be
chosen to be a relatively large value (10 k
–100 k), and
the other feedback resistance, Ri, is calculated using stan-
dard op amp configuration gain equations. Most audio ampli-
fiers are designed from the non-inverting amplifier configura-
tion.
DESIGN A 40W/8
AUDIO AMPLIFIER
Given:
Power Output
40W
Load Impedance
8
Input Level
1V
(max)
Input Impedance
100 k
Bandwidth
20 Hz–20 kHz ±0.25 dB
Equations (5), (6) give:
40W/8
V
opeak = 25.3V
I
opeak = 3.16A
Therefore the supply required is: ±30.3V @3.16A
With 15% regulation and high line the final supply voltage is
±38.3V using Equation (7). At this point it is a good idea to
check the Power Output vs Supply Voltage to ensure that the
required output power is obtainable from the device while
maintaining low THD + N. It is also good to check the Power
Dissipation vs Supply Voltage to ensure that the device can
handle the internal power dissipation. At the same time de-
signing in a relatively practical sized heat sink with a low
thermal resistance is also important. Refer to Typical Per-
formance Characteristics graphs and the Thermal Con-
siderations section for more information.
The minimum gain from
Equation (8) is: A
V ≥ 18
We select a gain of 21 (Non-Inverting Amplifier); resulting in
a sensitivity of 894 mV.
Letting R
IN equal 100 k gives the required input imped-
ance, however, this would eliminate the “volume control” un-
less an additional input impedance was placed in series with
the 10 k
potentiometer that is depicted in Figure 1. Adding
the additional 100 k
resistor would ensure the minimum re-
quired input impedance.
For low DC offsets at the output we let R
f1 = 100 k. Solving
for Ri (Non-Inverting Amplifier) gives the following:
Ri=R
f1/(AV 1) = 100k/(21 1) = 5 k; use 5.1 k
The bandwidth requirement must be stated as a pole, i.e.,
the 3 dB frequency. Five times away from a pole give
0.17 dB down, which is better than the required 0.25 dB.
Therefore:
f
L =20 Hz/5=4 Hz
f
H = 20 kHz x 5 = 100 kHz
At this point, it is a good idea to ensure that the Gain Band-
width Product for the part will provide the designed gain out
to the upper 3 dB point of 100 kHz. This is why the minimum
GBWP of the LM3875 is important.
GBWP = A
V x f3 dB = 21 x 100 kHz = 2.1 MHz
GBWP = 2.0 MHz (min) for LM3875
LM3875
www.national.com
14
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM3875T | 功能描述:IC AMP AUDIO PWR 56W AB TO220-11 RoHS:是 类别:集成电路 (IC) >> 线性 - 音頻放大器 系列:Overture™ 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) |
| LM3875T | 制造商:Texas Instruments 功能描述:IC AMP AUDIO 100W 3875 SIL-11 |
| LM3875T/NOPB | 制造商:Texas Instruments 功能描述:Audio Amp Speaker 1-CH Mono 56W Class-AB 11-Pin(11+Tab) TO-220 |
| LM3875TF | 功能描述:音频放大器 RoHS:否 制造商:STMicroelectronics 产品:General Purpose Audio Amplifiers 输出类型:Digital 输出功率: THD + 噪声: 工作电源电压:3.3 V 电源电流: 最大功率耗散: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:TQFP-64 封装:Reel |
| LM3875TF/NOPB | 功能描述:音频放大器 RoHS:否 制造商:STMicroelectronics 产品:General Purpose Audio Amplifiers 输出类型:Digital 输出功率: THD + 噪声: 工作电源电压:3.3 V 电源电流: 最大功率耗散: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:TQFP-64 封装:Reel |
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