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參數(shù)資料
| 型號： | LM4876 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | 1.1W Audio Power Amplifier with Shutdown Logic Low |
| 中文描述： | 1.1W音頻功率放大器，帶有關斷邏輯低 |
| 文件頁數(shù)： | 7/9頁 |
| 文件大?。?/td> | 247K |
| 代理商： | LM4876 |
Application Information
(Continued)
current draw will be minimized in idle mode. While the device
will be disabled with shutdown pin voltages less than 0.4
V
, the idle current may be greater than the typical value of
0.01 μA.
In many applications, a microcontroller or microprocessor
output is used to control the shutdown circuitry which pro-
vides a quick, smooth transition into shutdown.Another solu-
tion is to use a single-pole, single-throw switch in conjunction
with an external pull-down resistor. When the switch is open,
the shutdown pin (1) is connected to ground through the pull-
down resistor (R
) and the part is put into shutdown mode.
If the switch is closed, then V
is applied to the shutdown
pin and the LM4876 is enabled. This scheme guarantees
that the shutdown pin will not float thus preventing unwanted
state changes. If an Active Circuit is used to drive the shut-
down pin (1), then the pull-down resistor (R
PD
-20k) will not
be necessary.
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 LM4876 is tolerant of
external component combinations, consideration to compo-
nent values must be used to maximize overall system qual-
ity.
The LM4876 is unity-gain stable which gives a designer
maximum system flexibility. The LM4876 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 LM4876 turns
on. The slower the LM4876’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
equal to
1.0 μF is recommended in all but the most cost sensitive de-
signs.
L
www.national.com
7
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LM4876_03 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:1.1W Audio Power Amplifier with Logic Low Shutdown |
| LM4876M | 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 |
| LM4876M/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: 安裝風格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| LM4876MM | 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 |
| LM4876MM/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: 安裝風格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
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