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參數(shù)資料
| 型號： | LM4911 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Stereo 40mW Low Noise Headphone Amplifier with Selectable Capacitive Coupled or OCL Output |
| 中文描述： | 40mW的功率立體聲耳機放大器，低噪聲與耦合模式或無需輸出電容可選 |
| 文件頁數(shù)： | 16/18頁 |
| 文件大?。?/td> | 923K |
| 代理商： | LM4911 |
Application Information
(Continued)
MICRO POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the
LM4911’s shutdown function. Activate micro-power shut-
down by applying a logic-low voltage to the SHUTDOWN
pin. When active, the LM4911’s micro-power shutdown fea-
ture turns off the amplifier’s bias circuitry, reducing the sup-
ply current. The trigger point varies depending on supply
voltage and is shown in the Shutdown Hysteresis Voltage
graphs in the Typical Performance Characteristics section.
The low 0.1μA(typ) shutdown current is achieved by apply-
ing a voltage that is as near as ground as possible to the
SHUTDOWN pin. A voltage that is higher than ground may
increase the shutdown current. There are a few ways to
control the micro-power shutdown. These include using a
single-pole, single-throw switch, a microprocessor, or a mi-
crocontroller. When using a switch, connect an external
100k
pull-up resistor between the SHUTDOWN pin and
V
. Connect the switch between the SHUTDOWN pin and
ground. Select normal amplifier operation by opening the
switch. Closing the switch connects the SHUTDOWN pin to
ground, activating micro-power shutdown.
The switch and resistor guarantee that the SHUTDOWN pin
will not float. This prevents unwanted state changes. In a
system with a microprocessor or microcontroller, use a digi-
tal output to apply the control voltage to the SHUTDOWN
pin. Driving the SHUTDOWN pin with active circuitry elimi-
nates the pull-up resistor.
Shutdown enable/disable times are controlled by a combina-
tion of C
B
and V
DD
. Larger values of C
B
results in longer turn
on/off times from Shutdown. Smaller Vdd values also in-
crease turn on/off time for a given value of C
B
. Longer
shutdown times also improve the LM4911’s resistance to
click and pop upon entering or returning from shutdown. For
a 2.4V supply and C
= 4.7μF, the LM4911 requires about 2
seconds to enter or return from shutdown. This longer shut-
down time enables the LM4911 to have virtually zero pop
and click transients upon entering or release from shutdown.
Smaller values of C
will decrease turn-on time, but at the
cost of increased pop and click and reduced PSRR. Since
shutdown enable/disable times increase dramatically as
supply voltage gets below 2.2V, this reduced turn-on time
may be desirable if extreme low supply voltage levels are
used as this would offset increases in turn-on time caused by
the lower supply voltage. This technique is not recom-
mended for OCL mode since shutdown enable/disable times
are very fast (0.5s) independent of supply voltage.
MUTE
When in C-CUPL mode, the LM4911 also features a mute
function that enables extremely fast turn-on/turn-off with a
minimum of output pop and click with a low current con-
sumption (
≤
100μA). The mute function leaves the outputs at
their bias level, thus resulting in higher power consumption
than shutdown 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 techniques match those given for the shutdown
function as well.
The mute function is not necessary when the LM4911 is
operating in OCL mode since the shutdown function oper-
ates quickly in OCL mode with less power consumption than
mute.
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 us-
ing integrated power amplifiers is critical to optimize device
and system performance. While the LM4911 is tolerant of
external component combinations, consideration to compo-
nent values must be used to maximize overall system qual-
ity.
The LM4911 is unity-gain stable which gives the designer
maximum system flexibility. The LM4911 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.
Input signals equal to or greater than 1V
are available
from sources such as audio codecs. Very large values
should not be used for the gain-setting resistors. Values for
R
and R
should be less than 1M
. Please refer to the
section,
Audio Power Amplifier Design
, for a more com-
plete 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 response 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 por-
table 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 frequency 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
. A larger input
coupling capacitor requires more charge to reach its quies-
cent DC voltage. This charge comes from the output via the
feedback Thus, by minimizing the capacitor size based on
necessary low frequency response, turn-on time can be
minimized. A small value of C
i
(in the range of 0.1μF to
0.39μF), is recommended.
AUDIO POWER AMPLIFIER DESIGN
A 25mW/32
Audio Amplifier
Given:
Power Output
Load Impedance
Input Level
Input Impedance
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
25mWrms
32
1Vrms
20k
L
www.national.com
16
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM4911LD | 制造商:NSC 制造商全稱: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 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(biāo)準(zhǔn)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(fù)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(hù)，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) |
| LM4911LDX | 功能描述:IC AMP AUDIO PWR .145W AB 10LLP 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(biāo)準(zhǔn)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(fù)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(hù)，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) |
| LM4911MM | 功能描述:音頻放大器 RoHS:否 制造商:STMicroelectronics 產(chǎn)品:General Purpose Audio Amplifiers 輸出類型:Digital 輸出功率: THD + 噪聲: 工作電源電壓:3.3 V 電源電流: 最大功率耗散: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| LM4911MM/NOPB | 功能描述:音頻放大器 RoHS:否 制造商:STMicroelectronics 產(chǎn)品:General Purpose Audio Amplifiers 輸出類型:Digital 輸出功率: THD + 噪聲: 工作電源電壓:3.3 V 電源電流: 最大功率耗散: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
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