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参数资料
| 型号： | LM4912MM/NOPB |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 音频／视频放大 |
| 英文描述： | 0.145 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO10 |
| 封装： | MSOP-10 |
| 文件页数： | 5/16页 |
| 文件大小： | 490K |
| 代理商： | LM4912MM/NOPB |
MUTE
When in C-CUPL mode, the LM4912 also features a mute
function that is independent of load impedance and enables
extremely fast turn-on/turn-off with a minimum of output pop
and click. The mute function leaves the outputs at their bias
level, thus resulting in higher power consumption than shut-
down mode, but also provides much faster turn on/off times.
Mute mode is enabled by providing a logic high signal on the
MUTE pin in the opposite manner as the shutdown function
described above. Threshold voltages and activation tech-
niques match those given for the shutdown function as well.
Additionally, Mute should not be enabled during shutdown or
while entering or returning from shutdown. This is not a valid
operation condition and may result in much higher pop and
click values.
PROPER SELECTION OF EXTERNAL COMPONENTS
Proper selection of external components in applications using
integrated power amplifiers is critical to optimize device and
system performance. While the LM4912 is tolerant of external
component combinations, consideration to component values
must be used to maximize overall system quality.
The LM4912 is unity-gain stable which gives the designer
maximum system flexibility. The LM4912 should be used in
low gain configurations to minimize THD+N values, and max-
imize the signal to noise ratio. Low gain configurations require
large input signals to obtain a given output power. Input sig-
nals equal to or greater than 1V
rms are available from sources
such as audio codecs. Very large values should not be used
for the gain-setting resistors. Values for R
i and Rf should be
less than 1M
. Please refer to the section, Audio Power
Amplifier Design
, for a more complete explanation of proper
gain selection
Besides gain, one of the major considerations is the closed-
loop bandwidth of the amplifier. To a large extent, the band-
width is dictated by the choice of external components shown
in Figures 2 and 3. The input coupling capacitor, C
i, forms a
first order high pass filter which limits low frequency response.
This value should be chosen based on needed frequency re-
sponse and turn-on time.
SELECTION OF INPUT CAPACITOR SIZE
Amplifying the lowest audio frequencies requires a high value
input coupling capacitor, C
i. A high value capacitor can be
expensive and may compromise space efficiency in portable
designs. In many cases, however, the headphones used in
portable systems have little ability to reproduce signals below
60Hz. Applications using headphones with this limited fre-
quency response reap little improvement by using a high
value input capacitor.
In addition to system cost and size, turn on time is affected by
the size of the input coupling capacitor C
i. A larger input cou-
pling capacitor requires more charge to reach its quiescent
DC voltage. This charge comes from the output via the feed-
back Thus, by minimizing the capacitor size based on nec-
essary low frequency response, turn-on time can be mini-
mized. A small value of C
i (in the range of 0.1F to 0.39F),
is recommended.
AUDIO POWER AMPLIFIER DESIGN
A 25mW/32
Audio Amplifier
Given:
Power Output
25mWrms
Load Impedance
32
Input Level
1Vrms
Input Impedance
20k
A designer must first determine the minimum supply rail to
obtain the specified output power. By extrapolating from the
Output Power vs Supply Voltage graphs in the Typical Per-
formance Characteristics
section, the supply rail can be
easily found.
3V is a standard voltage in most applications, it is chosen for
the supply rail. Extra supply voltage creates headroom that
allows the LM4912 to reproduce peak in excess of 25mW
without producing audible distortion. At this time, the designer
must make sure that the power supply choice along with the
output impedance does not violate the conditions explained
in the Power Dissipation section.
Once the power dissipation equations have been addressed,
the required gain can be determined from Equation 2.
(3)
From Equation 4, the minimum A
V is 0.89; use AV = 1. Since
the desired input impedance is 20k
, and with a A
V gain of 1,
a ratio of 1:1 results from Equation 1 for R
f to Ri. The values
are chosen with R
i = 20k and Rf = 20k. The final design
step is to address the bandwidth requirements which must be
stated as a pair of -3dB frequency points. Five times away
from a -3dB point is 0.17dB down from passband response
which is better than the required ± 0.25dB specified.
f
L = 100Hz/5 = 20Hz
f
H = 20kHz * 5 = 100kHz
As stated in the External Components section, R
i in con-
junction with C
i creates a
C
i ≥ 1 / (2π * 20k * 20Hz) = 0.397F; use 0.39F.
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 LM4912 GBWP of 10MHz.
This figure displays that is a designer has a need to design
an amplifier with higher differential gain, the LM4912 can still
be used without running into bandwidth limitations.
Revision History
Rev
Date
Description
1.0
7/15/05
Fixed spelling typos.
1.01
06/16/08
Fixed a typo.
13
www.national.com
LM4912
相关PDF资料 |
PDF描述 |
|---|---|
| LM581JH | 1-OUTPUT THREE TERM VOLTAGE REFERENCE, 10 V, MBCY3 |
| LM581TH | 1-OUTPUT THREE TERM VOLTAGE REFERENCE, 10 V, MBCY3 |
| LM6181IM/NOPB | VIDEO AMPLIFIER, PDSO16 |
| LM8500HVA9/NOPB | SPECIALTY CONSUMER CIRCUIT, PQCC44 |
| LM8500IMT9/NOPB | SPECIALTY CONSUMER CIRCUIT, PDSO48 |
相关代理商/技术参数 |
参数描述 |
|---|---|
| LM4912MMX/NOPB | 功能描述:IC AMP AUDIO PWR .145W AB 10MSOP 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) |
| LM4913 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:2W Monaural, 90mW Stereo Headphone Audio Amplifier |
| LM4913A WAF | 制造商:Texas Instruments 功能描述: |
| LM4913MH | 制造商:Rochester Electronics LLC 功能描述: 制造商:Texas Instruments 功能描述: |
| LM4913MH/NOPB | 功能描述:IC AMP AUDIO MONO/STER 10TSSOP 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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