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參數(shù)資料
| 型號： | LM4850 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Mono 1.5 W / Stereo 300 mW Power Amplifier |
| 中文描述： | 單聲道1.5瓦/ 300毫瓦立體聲功率放大器 |
| 文件頁數(shù)： | 13/20頁 |
| 文件大小： | 1112K |
| 代理商： | LM4850 |
Application Information
(Continued)
Also shown in
Figure 2
are the electrical connections for the
headphone jack and plug. A 3-wire plug consists of a Tip,
Ring, and Sleave, where the Tip and Ring are audio signal
conductors and the Sleave is the common ground return.
One control pin for each headphone jack is sufficient to
indicate to the control inputs that a user has inserted a plug
into the jack and that the headphone mode of operation is
desired.
To ensure smooth transition from BTL to SE operation, it is
important to connect HP-IN and R
PU1
to the control pin on
the Right Output of the headphone jack. The control pin on
the Left Output of the headphone jack should be left open.
Connecting the node between the HP-IN and R
PU1
to the
Left Output control pin may cause unwanted state changes
to the HP-IN pin.
PROPER SELECTION OF EXTERNAL COMPONENTS
Proper selection of external components in applications us-
ing integrated power amplifiers is critical for optimum device
and system performance. While the LM4850 is tolerant to a
variety of external component combinations, consideration
must be given to the external component values that maxi-
mize overall system quality.
The LM4850’s unity-gain stability allows a designer to maxi-
mize system performance. The LM4850’s gain should be set
no higher than necessary for any given application. A low
gain configuration maximizes signal-to-noise performance
and minimizes THD+N. However, a low gain configuration
also requires large input signals to obtain a given output
power. Input signals equal to or greater than 1V
are
available from sources such as audio codecs. Please refer to
the section,
Audio Power Amplifier Design
, for a more
complete explanation of proper gain selection.
Selecting Input and Output Capacitor Values
Besides gain, one of the major considerations is the
closed-loop bandwidth of the amplifier. To a large extent, the
bandwidth is dictated by the choice of external components
shown in
Figure 1
. The input coupling capacitor C
I
and
resistor R
I
form a first order high pass filter that limits low
frequency response. C
I
’s value should be based on the
desired frequency response weighed against the following:
Large value input and output capacitors are both expensive
and space consuming for portable designs. Clearly a certain
sized capacitor is needed to couple in low frequencies with-
out severe attenuation. But in many cases the speakers
used in portable systems, whether internal or external, have
little ability to reproduce signals below 150Hz. Thus, large
value input and output capacitors may not increase system
performance.
AUDIO POWER AMPLIFIER DESIGN
Design a 1W / 8
Bridged Audio Amplifier
Given:
Power Output:
Load Impedance
Input Level:
Input Impedance:
Bandwidth:
1W
RMS
8
1V
RMS
20k
100Hz - 20kHz
±
0.25dB
A designer must first determine the minimum supply voltage
needed to obtain the specified output power. By extrapolat-
ing from the Output Power vs Supply Voltage graphs in the
Typical Performance Characteristics
section, the supply
rail can be easily found. A second way to determine the
minimum supply rail is to calculate the required V
using Equation 5 and add the dropout voltage. This results in
Equation 6, where V
and V
are extrapolated
from the Dropout Voltage vs Supply Voltage curve in the
Typical Performance Characteristics
section.
(5)
V
DD
≥
(V
OPEAK
+ (V
ODTOP
+ V
ODBOT
))
(6)
Using the Output Power vs Supply Voltage graph for an 8
load, the minimum supply rail is 4.7V. But since 5V is a
standard supply voltage in most applications, it is chosen for
the supply rail. Extra supply voltage creates headroom that
allows the LM4850 to reproduce peaks in excess of 1W
without producing audible distortion. However, the designer
must make sure that the chosen power supply voltage and
output load does not violate the conditions explained in the
Power Dissipation
section.
Once the power dissipation equations have been addressed,
the required differential gain can be determined from Equa-
tion 7.
(7)
R
F
/ R
I
= A
VD
/ 2
(8)
From Equation 6, the minimum A
VD
is 2.83; use A
VD
= 3.
The desired input impedance was 20k
, and with an A
VD
of
3, using Equation 8 results in an allocation of R
I
= 20k
and
R
F
= 30k
.
The final design step is to set the amplifier’s 3dB frequency
bandwidth. To achieve the desired
±
0.25dB pass band
magnitude variation limit, the low frequency response must
20001050
FIGURE 2. Headphone Control Circuit
L
www.national.com
13
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| LM4850LD | Mono 1.5 W / Stereo 300 mW Power Amplifier |
| LM4850MM | Mono 1.5 W / Stereo 300 mW Power Amplifier |
| LM4850MT | Mono 1.5 W / Stereo 300 mW Power Amplifier |
| LM4851 | Integrated Audio Amplifier System |
| LM4851LQ | Integrated Audio Amplifier System |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM4850A E WAF | 制造商:Texas Instruments 功能描述: |
| LM4850LD | 制造商:Rochester Electronics LLC 功能描述:1.5W MON AUD&95MW HEADPHN AMP - Bulk |
| LM4850LDX | 制造商:Rochester Electronics LLC 功能描述:1.5W MON AUD&95MW HEADPHN AMP - Bulk |
| LM4850MM | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Mono 1.5 W / Stereo 300 mW Power Amplifier |
| LM4850MM/NOPB | 功能描述:IC AMP AUDIO PWR 1.9W AB 10MSOP RoHS:是 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:Boomer® 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:2,500 系列:DirectDrive® 類型:H 類 輸出類型:耳機，2-通道（立體聲） 在某負載時最大輸出功率 x 通道數(shù)量:35mW x 2 @ 16 歐姆 電源電壓:1.62 V ~ 1.98 V 特點:I²C，麥克風(fēng)，靜音，短路保護，音量控制 安裝類型:表面貼裝 供應(yīng)商設(shè)備封裝:25-WLP（2.09x2.09） 封裝/外殼:25-WFBGA，WLCSP 包裝:帶卷 (TR) |
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