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参数资料
| 型号： | LM4910MMX/NOPB |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 音频／视频放大 |
| 英文描述： | 0.035 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO8 |
| 封装： | MSOP-8 |
| 文件页数： | 4/22页 |
| 文件大小： | 828K |
| 代理商： | LM4910MMX/NOPB |
Application Information (Continued)
From Equation 2, the minimum A
V is 0.98; use AV = 1. Since
the desired input impedance is 20k
, and with A
V equal to 1,
a ratio of 1:1 results from Equation 1 for R
f to Ri. The values
are chosen with R
i = 20k
and R
f = 20k
.
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
(3)
and an
f
H = 20kHzx5= 100kHz
(4)
As mentioned in the Selecting Proper External Compo-
nents section, R
i and Ci create a highpass filter that sets the
amplifier’s lower bandpass frequency limit. Find the coupling
capacitor’s value using Equation (3).
C
i
≥ 1/(2πR
ifL)
(5)
The result is
1/(2
π*20k*20Hz) = 0.397F
Use a 0.39F capacitor, the closest standard value.
The high frequency pole is determined by the product of the
desired frequency pole, f
H, and the differential gain, AV. With
an A
V = 1 and fH = 100kHz, the resulting GBWP = 100kHz
which is much smaller than the LM4910 GBWP of 11MHz.
This figure displays that if a designer has a need to design
an amplifier with higher differential gain, the LM4910 can still
be used without running into bandwidth limitations.
MINIMIZING OUTPUT NOISE / REDUCING OUTPUT POWER
Output noise delivered to the load can be minimized with the
use of an external resistor, R
SERIES, placed in series with
each load as shown in Figure 3.R
SERIES forms a voltage
divider with the impedance of the headphone driver R
L.As a
result, output noise is attenuated by the factor R
L /(RL +
R
SERIES). Figure 4 illustrates the relationship between output
noise and R
SERIES for different loads. RSERIES also de-
creases output power delivered to the load by the factor R
L
/(R
L +RSERIES)
2. However, this may not pose a problem
since most headphone applications require less than 10mW
THD+N) vs R
SERIES for different loads.
Figure 4 shows an optional resistor connected between the
amplifier output that drives the headphone jack sleeve and
ground. This resistor provides a ground path that supressed
power supply hum. This hum may occur in applications such
as notebook computers in a shutdown condition and con-
nected to an external powered speaker. The resistor’s 100
value is a suggested starting point. Its final value must be
determined based on the tradeoff between the amount of
noise suppression that may be needed and minimizing the
additional current drawn by the resistor (25mA for a 100
resistor and a 5V supply).
20030568
FIGURE 3.
LM4910
www.national.com
12
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM4911 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:Stereo 40mW Low Noise Headphone Amplifier with Selectable Capacitive Coupled or OCL Output |
| LM4911LD | 制造商:NSC 制造商全称:National Semiconductor 功能描述:Stereo 40mW Low Noise Headphone Amplifier with Selectable Capacitive Coupled or OCL Output |
| LM4911LD/NOPB | 功能描述:IC AMP AUDIO PWR .145W AB 10LLP 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) |
| LM4911LDX | 功能描述:IC AMP AUDIO PWR .145W AB 10LLP 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) |
| LM4911MM | 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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