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參數(shù)資料
| 型號： | LM4880MWA |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 0.325 W, 2 CHANNEL, AUDIO AMPLIFIER, UUC |
| 封裝： | WAFER |
| 文件頁數(shù)： | 15/15頁 |
| 文件大小： | 418K |
| 代理商： | LM4880MWA |
Application Information (Continued)
The operation of this circuit is rather simple. With the switch
closed, R
p and Ro form a resistor divider which produces a
gate voltage of less than 5 mV. This gate voltage keeps the
NMOS inverter off and R
sd pulls the shutdown pin of the
LM4880 to the supply voltage. This places the LM4880 in
shutdown mode which reduces the supply current to 0.7 A
typically. When the switch is open, the opposite condition is
produced. Resistor R
p pulls the gate of the NMOS high
which turns on the inverter and produces a logic low signal
on the shutdown pin of the LM4880. This state enables the
LM4880 and places the amplifier in its normal mode of op-
eration.
This type of circuit is clearly valuable in portable products
where battery life is critical, but is also benefical for power
conscious designs such as “Green PC’s”.
AUTOMATIC SWITCHING CIRCUIT
A circuit closely related to the Automatic Shutdown Circuit
is the Automatic Switching Circuit of
Figure 3. The Auto-
matic Switching Circuit utilizes both the input and output of
the NMOS inverter to toggle the states of two different audio
power amplifiers. The LM4880 is used to drive stereo single
ended loads, while the LM4861 drives bridged internal
speakers.
In this application, the LM4880 and LM4861 are never on at
the same time. When the switch inside the headphone jack
is open, the LM4880 is enabled and the LM4861 is disabled
since the NMOS inverter is on. If a headphone jack is not
present, it is assumed that the internal speakers should be
on and thus the voltage on the LM4861 shutdown pin is low
and the voltage at the LM4880 pin is high. This results in the
LM4880 being shutdown and the LM4861 being enabled.
Only one channel of this circuit is shown in
Figure 3 to keep
the drawing simple but the typical application would a
LM4880 driving a stereo external headphone jack and two
LM4861’s driving the internal stereo speakers. If only one in-
ternal speaker is required, a single LM4861 can be used as
a summer to mix the left and right inputs into a single mono
channel.
PROPER SELECTION OF EXTERNAL COMPONENTS
Selection of external components when using integrated
power amplifiers is critical to optimize device and system
performance. While the LM4880 is tolerant of external com-
ponent combinations, care must be exercised when choos-
ing component values.
The LM4880 is unity-gain stable which gives a designer
maximum system flexibility. The LM4880 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 design 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. Both the input coupling capacitor, C
i, and
the output coupling capacitor, C
o, form first order high pass
filters which limit low frequency response. These values
should be chosen based on needed frequency response for
a few distinct reasons.
Selection of Input and Output Capacitor Size
Large input and output capacitors are both expensive and
space hungry for portable designs. Clearly a certain sized
capacitor is needed to couple in low frequencies without se-
vere attenuation. But in many cases the transducers used in
portable systems, whether internal or external, have little
ability to reproduce signals below 100 Hz–150 Hz. Thus us-
ing large input and output capacitors may not increase sys-
tem performance.
In addition to system cost and size, click and pop perfor-
mance is effected by the size of the input coupling capacitor,
C
i. A larger input coupling capacitor requires more charge to
reach its quiescent DC voltage (normally 1/2 V
DD.) 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 and output capacitor sizes,
careful consideration should be paid to the bypass capacitor
size. The bypass capacitor, C
B, is the most critical compo-
nent to minimize turn-on pops since it determines how fast
the LM4880 turns on. The slower the LM4880’s outputs
ramp to their quiescent DC voltage (nominally 1/2 V
DD), the
smaller the turn-on pop. Choosing C
B equal to 1.0 F along
with a small value of C
i (in the range of 0.1 F to 0.39 F),
should produce a virtually clickless and popless shutdown
function. While the device will function properly, (no oscilla-
tions or motorboating), with C
B equal to 0.1 F, the device
will be much more susceptible to turn-on clicks and pops.
Thus, a value of C
B equal to 1.0 F or larger is recom-
mended in all but the most cost sensitive designs.
AUDIO POWER AMPLIFIER DESIGN
Design a Dual 200 mW/8
Audio Amplifier
Given:
Power Output:
200 mWrms
Load Impedance:
8
Input Level:
1 Vrms (max)
Input Impedance:
20 k
Bandwidth:
100 Hz–20 kHz ± 0.50 dB
A designer must first determine the needed supply rail to ob-
tain the specified output power. Calculating the required sup-
ply rail involves knowing two parameters, V
opeak and also the
dropout voltage. As shown in the Typical Performance
Curves, the dropout voltage is typically 0.5V. V
opeak can be
determined from
Equation (3).
(3)
For 200 mW of output power into an 8
load, the required
V
opeak is 1.79V. Since this is a single supply application, the
minimum supply voltage is twice the sum of V
opeak and Vod.
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 LM4880 to reproduce peaks in ex-
cess of 200 mW without clipping the signal. 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. Remember that
the maximum power dissipation value from
Equation (1)
must be multiplied by two since there are two independent
amplifiers inside the package.
Once the power dissipation equations have been addressed,
the required gain can be determined from
Equation (4).
LM4880
www.national.com
9
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM4880MX | 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: 安裝風格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| LM4880MX/NOPB | 功能描述:音頻放大器 Dual 200 mW Audio Pwr Amp 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: 安裝風格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| LM4880N | 功能描述:IC AMP AUDIO PWR .325W STER 8DIP RoHS:否 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，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) |
| LM4880-SH2-R | 制造商:UTC-IC 制造商全稱:UTC-IC 功能描述:DUAL 250mW AUDIO POWER AMPLIFIER WITH SHUTDOWN MODE |
| LM4880-SH2-T | 制造商:UTC-IC 制造商全稱:UTC-IC 功能描述:DUAL 250mW AUDIO POWER AMPLIFIER WITH SHUTDOWN MODE |
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