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參數資料
| 型號： | LM4980SD |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 2 Cell Battery, 1mA, 42mW Per Channel High Fidelity Stereo Headphone Audio Amplifier for MP3 players |
| 中文描述： | 0.042 W, 2 CHANNEL, AUDIO AMPLIFIER, DSO10 |
| 封裝： | LLP-10 |
| 文件頁數： | 13/20頁 |
| 文件大?。?/td> | 1324K |
| 代理商： | LM4980SD |
Application Information
AMPLIFIER CONFIGURATION
As shown in Figure 1, the LM4980 consists of a stereo pair
of audio amplifiers. These amplifiers operate on a single
supply and have single-ended inputs and outputs. The qui-
escent operating point of each amplifier input and output is
equal to the voltage applied to the V
MID
pin (usually V
DD
/2).
C
MIDCAP
VALUE SELECTION
Careful consideration should be paid to value of C
MIDCAP
,
the capacitor connected between the MIDCAP pin and
ground. The value of C
MIDCAP
determines how fast the
LM4980 settles to quiescent operation and determines the
amount of output transient suppression. Choosing C
equal to 4.7μF along with a small value of C
(in the range
of 0.1μF to 1.0μF), produces shutdown function that is es-
sentially output-transient free. Choosing C
no larger than
necessary for the desired bandwidth helps minimize clicks
and pops. This ensures that output transients are minimized
when power is first applied or the LM4980 resumes opera-
tion after shutdown. The MIDCAP offers the following ben-
efits: better linearity for reduced THD+N, reduced channel-
to-channel crosstalk, and less susceptibility to ground noise.
For the ultimate suppression of output transient when power
is applied or removed, ensure that the voltage applied to the
SHDN pin is a logic low. This will activate the micro-power
shutdown.
OPTIMIZING OUTPUT-GROUND NOISE REDUCTION
In addition to the output-ground noise reduction afforded by
C
, further reduction can be achieved by the inclusion
of a ferrite bead. The ferrite bead (FB) is placed between
ground and common connection between the C
MIDCAP
and
the headphone ground connection. This is shown in Figure
3. The ferrite bead is beneficial in environments where the
headphone and C
MIDCAP
ground connection is shared with
circuitry (such as video) that may inject noise on a common
ground.
OPTIMIZING OUTPUT TRANSIENT SUPPRESSION
The LM4980 contains circuitry that eliminates turn-on and
shutdown output transients ("clicks and pops"). For this dis-
cussion, turn-on refers to either applying the power supply
voltage or when the micro-power shutdown mode is deacti-
vated. The turn-on time delay is the time duration that occurs
between the application of the power supply voltage or de-
activating shutdown and when the applied input signal ap-
pears at the amplifier outputs.
C
’s value plays a significant role in the suppression of
output transients. The amount of suppression increases as
C
MIDCAP
’s value increases. However, changing the value of
C
alters the LM4980’s turn-on time. There is a linear
relationship between the value of C
and the turn-on
time. Here are some typical turn-on times for various values
of C
MIDCAP
.
TABLE 1. Typical turn-on time versus C
MIDCAP
value
C
MIDCAP
VALUE (μF)
4.7
6.8
10.0
Turn-On Time (ms)
250
360
530
STAND-ALONE V
MID
VOLTAGE GENERATION
The LM4980 is designed to take advantage of audio DACs
(digital-to-analog converters) and other signal sources that,
in addition to generating an analog signal, also create an AC
ground potential. This AC ground potential is typically V
DD
/2.
This V
DD
/2 is applied to the LM4980’s V
MID
pin (pin 4).
Using two external resistors allows the LM4980 to be easily
used in applications where the V
MID
voltage is not internally
generated and supplied to the LM4980 by other circuits.
Figure 4 shows this configuration.
SELECTING THE OUTPUT COUPLING CAPACITOR
VALUE
To ensure that no performance degrading DC current flows
through the load (something with which speakers would just
as soon not have to tolerate), coupling capacitors are nec-
essary between the amplifier output pins and the load. Be-
sides blocking DC current, the output coupling capacitor
value, together with the load resistance, produces a low
frequency amplitude rolloff, whose cutoff frequency is found
using Equation 1.
(1)
When driving 32
headphones, the 220μF C
ca-
pacitors shown in Figure 2 produce a cutoff frequency equal
to 23Hz.
The output coupling capacitors also influence the output
transient behavior at power-up and when activating or deac-
20142981
FIGURE 3. Adding a ferrite bead improves
ground-noise suppression
20142980
FIGURE 4. Simple circuit generates LM4980’s V
MID
voltage
L
www.national.com
13
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相關代理商/技術參數 |
參數描述 |
|---|---|
| LM4980SD/NOPB | 功能描述:音頻放大器 RoHS:否 制造商:STMicroelectronics 產品: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 |
| LM4980SDBD | 功能描述:音頻 IC 開發(fā)工具 LM4980 EVAL BOARD RoHS:否 制造商:Texas Instruments 產品:Evaluation Kits 類型:Audio Amplifiers 工具用于評估:TAS5614L 工作電源電壓:12 V to 38 V |
| LM4980SDX | 功能描述:音頻放大器 RoHS:否 制造商:STMicroelectronics 產品: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 |
| LM4980SDX/NOPB | 功能描述:音頻放大器 RoHS:否 制造商:STMicroelectronics 產品: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 |
| LM4981 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Ground-Referenced, 80mW Stereo Headphone Amplifier with Digital Volume Control |
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