- 您现在的位置：买卖IC网 > PDF目录30754 > LM4866MT/NOPB (NATIONAL SEMICONDUCTOR CORP) 1.5 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO20 PDF资料下载
参数资料
| 型号： | LM4866MT/NOPB |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 音频／视频放大 |
| 英文描述： | 1.5 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO20 |
| 封装： | 4.40 MM, TSSOP-20 |
| 文件页数： | 5/21页 |
| 文件大小： | 1013K |
| 代理商： | LM4866MT/NOPB |
Application Information (Continued)
SELECTING PROPER EXTERNAL COMPONENTS
Optimizing the LM4866’s performance requires properly se-
lecting external components. Though the LM4866 operates
well when using external components with wide tolerances,
best performance is achieved by optimizing component val-
ues.
The LM4866 is unity-gain stable, giving a designer maximum
design flexibility. The gain should be set to no more than a
given application requires. This allows the amplifier to
achieve minimum THD+N and maximum signal-to-noise ra-
tio. These parameters are compromised as the closed-loop
gain increases. However, low gain demands input signals
with greater voltage swings to achieve maximum output
power. Fortunately, many signal sources such as audio CO-
DECs have outputs of 1V
RMS (2.83VP-P). Please refer to the
Audio Power Amplifier Design section for more informa-
tion on selecting the proper gain.
Input Capacitor Value Selection
Amplifying the lowest audio frequencies requires high value
input coupling capacitor (C
i in Figure 1). A high value capaci-
tor can be expensive and may compromise space efficiency
in portable designs. In many cases, however, the speakers
used in portable systems, whether internal or external, have
little ability to reproduce signals below 150Hz. Applications
using speakers with this limited frequency response reap
little improvement by using large input capacitor.
Besides effecting system cost and size, C
i has an affect on
the LM4866’s click and pop performance. When the supply
voltage is first applied, a transient (pop) is created as the
charge on the input capacitor changes from zero to a quies-
cent state. The magnitude of the pop is directly proportional
to the input capacitor’s size. Higher value capacitors need
more time to reach a quiescent DC voltage (usually V
DD/2)
when charged with a fixed current. The amplifier’s output
charges the input capacitor through the feedback resistor,
R
f. Thus, pops can be minimized by selecting an input
capacitor value that is no higher than necessary to meet the
desired -3dB frequency.
A shown in Figure 1, the input resistor (R
I) and the input
capacitor, C
I produce a 3dB high pass filter cutoff frequency
that is found using Equation (7).
(7)
As an example when using a speaker with a low frequency
limit of 150Hz, C
I, using Equation (4), is 0.063F. The 1.0F
C
I shown in Figure 1 allows the LM4866 to drive high effi-
ciency, full range speaker whose response extends below
30Hz.
Bypass Capacitor Value Selection
Besides minimizing the input capacitor size, careful consid-
eration should be paid to value of C
B, the capacitor con-
nected to the BYPASS pin. Since C
B determines how fast
the LM4866 settles to quiescent operation, its value is critical
when minimizing turnon pops. The slower the LM4866’s
outputs ramp to their quiescent DC voltage (nominally 1/2
V
DD), the smaller the turnon pop. Choosing CB equal to
1.0F along with a small value of C
i (in the range of 0.1F to
0.39F), produces a click-less and pop-less shutdown func-
tion. As discussed above, choosing C
i no larger than neces-
sary for the desired bandwidth helps minimize clicks and
pops.
OPTIMIZING CLICK AND POP REDUCTION PERFOR-
MANCE
The LM4866 contains circuitry to minimize turn-on and shut-
down transients or "clicks and pop". For this discussion,
turn-on refers to either applying the power supply voltage or
when the shutdown mode is deactivated. While the power
supply is ramping to its final value, the LM4866’s internal
amplifiers are configured as unity gain buffers. An internal
current source changes the voltage of the BYPASS pin in a
controlled, linear manner. Ideally, the input and outputs track
the voltage applied to the BYPASS pin. The gain of the
internal amplifiers remains unity until the voltage on the
bypass pin reaches 1/2 V
DD. As soon as the voltage on the
BYPASS pin is stable, the device becomes fully operational.
Although the bypass pin current cannot be modified, chang-
ing the size of C
B alters the device’s turn-on time and the
magnitude of "clicks and pops". Increasing the value of C
B
reduces the magnitude of turn-on pops. However, this pre-
sents a tradeoff: as the size of C
B increases, the turn-on time
increases. There is a linear relationship between the size of
C
B and the turn-on time. Here are some typical turn-on times
for various values of C
B:
C
B
T
ON
0.01F
20 ms
0.1F
200 ms
0.22F
440 ms
0.47F
940 ms
1.0F
2 Sec
In order eliminate "clicks and pops", all capacitors must be
discharged before turn-on. Rapidly switching V
DD may not
allow the capacitors to fully discharge, which may cause
"clicks and pops".
NO LOAD STABILITY
The LM4866 may exhibit low level oscillation when the load
resistance is greater than 10k
. This oscillation only occurs
as the output signal swings near the supply voltages. Pre-
vent this oscillation by connecting a 5k
between the output
pins and ground.
LM4866
www.national.com
13
相关PDF资料 |
PDF描述 |
|---|---|
| LM4866LQ/NOPB | 3.2 W, 2 CHANNEL, AUDIO AMPLIFIER, PQCC24 |
| LM4866LQX/NOPB | 3.2 W, 2 CHANNEL, AUDIO AMPLIFIER, PQCC24 |
| LM4866MTX/NOPB | 1.5 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO20 |
| LM4868MTE/NOPB | 3 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO20 |
| LM4868MTEX/NOPB | 3 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO20 |
相关代理商/技术参数 |
参数描述 |
|---|---|
| LM4867 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:Output-Transient-Free Dual 2.1W Audop Amplifier Plus No Coupling Capacitor Stereo Headphone Function |
| LM4867_02 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:Output-Transient-Free Dual 2.1W Audop Amplifier Plus No Coupling Capacitor Stereo Headphone Function |
| LM4867A E WAF | 制造商:Texas Instruments 功能描述: |
| LM4867LQ | 功能描述:IC AMP AUDIO PWR 3W STER 24LLP RoHS:否 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) |
| LM4867LQ/NOPB | 制造商:Texas Instruments 功能描述:Audio Amp Headphone/Speaker 2-CH Stereo 3W Class-AB 24-Pin LLP EP T/R |
发布紧急采购，3分钟左右您将得到回复。