- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄358866 > LM4871N (NATIONAL SEMICONDUCTOR CORP) 1.1W Audio Power Amplifier with Shutdown Mode PDF資料下載
參數(shù)資料
| 型號： | LM4871N |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 1.1W Audio Power Amplifier with Shutdown Mode |
| 中文描述： | 1.5 W, 1 CHANNEL, AUDIO AMPLIFIER, PDIP8 |
| 封裝： | DIP-8 |
| 文件頁數(shù)： | 6/8頁 |
| 文件大?。?/td> | 243K |
| 代理商： | LM4871N |
Application Information
(Continued)
external component combinations, consideration to compo-
nent values must be used to maximize overall system qual-
ity.
The LM4871 is unity-gain stable which gives a designer
maximum system flexibility. The LM4871 should be used in
low gain configurations to minimize THD+N values, and
maximize the signal to noise ratio. Low gain configurations
require large input signals to obtain a given output power. In-
put signals equal to or greater than 1 Vrms are available
from sources such as audio codecs. Please refer to the sec-
tion,
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 Figure 1 The input coupling capacitor, C
, forms a
first order high pass filter which limits low frequency re-
sponse. This value should be chosen based on needed fre-
quency response for a few distinct reasons.
Selection Of Input Capacitor Size
Large input capacitors are both expensive and space hungry
for portable designs. Clearly, a certain sized capacitor is
needed to couple in low frequencies without severe attenua-
tion. But in many cases the speakers used in portable sys-
tems, whether internal or external, have little ability to repro-
duce signals below 100 Hz to 150 Hz. Thus, using a large
input capacitor may not increase actual system perfor-
mance.
In addition to system cost and size, click and pop perfor-
mance is effected by the size of the input coupling capacitor,
C
A larger input coupling capacitor requires more charge to
reach its quiescent DC voltage (nominally 1/2 V
). This
charge comes from the output via the feedback and is apt to
create pops upon device enable. Thus, by minimizing the ca-
pacitor size based on necessary low frequency response,
turn-on pops can be minimized.
Besides minimizing the input capacitor size, careful consid-
eration should be paid to the bypass capacitor value. Bypass
capacitor, C
, is the most critical component to minimize
turn-on pops since it determines how fast the LM4871 turns
on. The slower the LM4871’s outputs ramp to their quiescent
DC voltage (nominally 1/2 V
), the smaller the turn-on pop.
Choosing C
B
equal to 1.0 μF along with a small value of C
i
(in the range of 0.1 μF to 0.39 μF), should produce a virtually
clickless and popless shutdown function. While the device
will function properly, (no oscillations or motorboating), with
C
B
equal to 0.1 μF, the device will be much more susceptible
to turn-on clicks and pops. Thus, a value of C
B
equal to
1.0 μF is recommended in all but the most cost sensitive de-
signs.
AUDIO POWER AMPLIFIER DESIGN
Design a 1W/8
Audio Amplifier
Given:
Power Output
Load Impedance
Input Level
Input Impedance
Bandwidth
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. A second way to determine the minimum sup-
ply rail is to calculate the required V
using Equation 3
and add the output voltage. Using this method, the minimum
supply voltage would be (V
+ (V
+ V
)), where
V
and V
are extrapolated from the Dropout Volt-
age vs Supply Voltage curve in the
Typical Performance
Characteristics
section.
1 Wrms
8
1 Vrms
20 k
100 Hz–20 kHz
±
0.25 dB
(3)
Using the Output Power vs Supply Voltage graph for an 8
load, the minimum supply rail is 4.6V. But since 5V is a stan-
dard voltage in most applications, it is chosen for the supply
rail. Extra supply voltage creates headroom that allows the
LM4871 to reproduce peaks in excess of 1W without produc-
ing audible distortion. At this time, the designer must make
sure that the power supply choice along with the output im-
pedance 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 4.
(4)
R
f
/R
i
= A
VD
/2
(5)
From Equation 4, the minimum A
VD
is 2.83; use A
VD
= 3.
Since the desired input impedance was 20 k
, and with a
A
VD
impedance of 2, a ratio of 1.5:1 of R
f
to R
i
results in an
allocation of R
i
= 20 k
and R
f
= 30 k
. The final design step
is to address the bandwidth requirements which must be
stated as a pair of 3 dB frequency points. Five times away
from a 3 dB point is 0.17 dB down from passband response
which is better than the required
±
0.25 dB specified.
f
L
= 100 Hz/5 = 20 Hz
f
H
= 20 kHz * 5 = 100 kHz
As stated in the
External Components
section, R
i
in con-
junction with C
i
create a highpass filter.
C
i
≥
1/(2
π
*20 k
*20 Hz) = 0.397 μF; use 0.39 μF
The high frequency pole is determined by the product of the
desired frequency pole, f
, and the differential gain, A
.
With a A
= 3 and f
= 100 kHz, the resulting GBWP =
150 kHz which is much smaller than the LM4871 GBWP of
4 MHz. This figure displays that if a designer has a need to
design an amplifier with a higher differential gain, the
LM4871 can still be used without running into bandwidth limi-
tations.
L
www.national.com
6
相關PDF資料 |
PDF描述 |
|---|---|
| LM4871MX | 1.1W Audio Power Amplifier with Shutdown Mode |
| LM4871M | 1.1W Audio Power Amplifier with Shutdown Mode |
| LM4873MTE-1 | Dual 2.1W Audio Amplifier Plus Stereo Headphone Function |
| LM4873MT | Dual 2.1W Audio Amplifier Plus Stereo Headphone Function |
| LM4873MTE | Dual 2.1W Audio Amplifier Plus Stereo Headphone Function |
相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LM4872 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:1 Watt Audio Power Amplifier in micro SMD package |
| LM4872IBP | 功能描述:IC AMP AUDIO PWR 1W MONO 8USMD RoHS:否 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:Boomer® 產(chǎn)品培訓模塊: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，靜音，短路保護，音量控制 安裝類型:表面貼裝 供應商設備封裝:25-WLP（2.09x2.09） 封裝/外殼:25-WFBGA，WLCSP 包裝:帶卷 (TR) |
| LM4872IBPX | 功能描述:IC AMP AUDIO PWR 1W MONO 8USMD RoHS:是 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:Boomer® 產(chǎn)品培訓模塊: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，靜音，短路保護，音量控制 安裝類型:表面貼裝 供應商設備封裝:25-WLP（2.09x2.09） 封裝/外殼:25-WFBGA，WLCSP 包裝:帶卷 (TR) |
| LM4872ITP | 制造商:Texas Instruments 功能描述:AMP AUDIO 1W BOOMER SMD 4872 |
| LM4872ITP/NOPB | 功能描述:IC AMP AUDIO PWR 1W MONO 8USMD RoHS:是 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:Boomer® 產(chǎn)品培訓模塊: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，靜音，短路保護，音量控制 安裝類型:表面貼裝 供應商設備封裝:25-WLP（2.09x2.09） 封裝/外殼:25-WFBGA，WLCSP 包裝:帶卷 (TR) |
發(fā)布緊急采購，3分鐘左右您將得到回復。