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參數(shù)資料
| 型號： | LM4882 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | 250mW Audio Power Amplifier with Shutdown Mode |
| 中文描述： | 25萬千瓦音頻功率放大器關(guān)斷模式 |
| 文件頁數(shù)： | 9/12頁 |
| 文件大?。?/td> | 445K |
| 代理商： | LM4882 |
Application Information
(Continued)
vice or the shutdown function may cause the “click and pop”
circuitry to not operate fully, resulting in increased “click and
pop” noise.
The value of C
will also reflect turn-on pops. Clearly, a cer-
tain size for C
is needed to couple in low frequencies without
excessive attenuation. But in many cases, the speakers
used in portable systems have little ability to reproduce sig-
nals below 100 Hz to 150 Hz. In this case, using a large input
and output coupling capacitor may not increase system per-
formance. In most cases, choosing a small value of C
in the
range of 0.1 μF to 0.33 μF, along with C
equal to 1.0 μF
should produce a virtually clickless and popless turn-on. In
cases where C
is larger than 0.33 μF, it may be advanta-
geous to increase the value of C
. Again, it should be under-
stood that increasing the value of C
will reduce the “clicks
and pops” at the expense of a longer device turn-on time.
AUDIO POWER AMPLIFIER DESIGN
Design a 250 mW/8
Audio Amplifier
Given:
Power Output
Load Impedance
Input Level
Input Impedance
Bandwidth
250 mWrms
8
1 Vrms (max)
20 k
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
and also
the dropout voltage. The latter is typically 530mV and can be
found from the graphs in the
Typical Performance Charac-
teristics.
V
OPEAK
can be determined from Equation 3.
(3)
For 250 mW of output power into an 8
load, the required
V
is 2 volts. A minimum supply rail of 4.55V results
from adding V
and V
. 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
LM4882 to reproduce peaks in excess of 300 mW without
clipping the signal.At this time, the designer must make sure
that the power supply choice along with the output imped-
ance does not violate the conditions explained in the
Power
Dissipation
section.
Once the power dissipation equations have been addressed,
the required gain can be determined from Equation 4.
(4)
A
V
= R
f
/ R
i
(5)
From Equation 4, the minimum gain is:
A
V
= 1.4
Since the desired input impedance was 20 k
, and with a
gain of 1.4, a value of 28 k
is designated for R
, assuming
5% tolerance resistors. This combination results in a nominal
gain of 1.4. The final design step is to address the bandwidth
requirements which must be stated as a pair of 3 dB fre-
quency points. Five times away from a 3 dB point is 0.17 dB
down from passband response assuming a single pole roll-
off. As stated in the
External Components
section, both R
i
in conjunction with C
, and C
with R
, create first order high-
pass filters. Thus to obtain the desired frequency low re-
sponse of 100 Hz within
±
0.5 dB, both poles must be taken
into consideration. The combination of two single order filters
at the same frequency forms a second order response. This
results in a signal which is down 0.34 dB at five times away
from the single order filter 3 dB point. Thus, a frequency of
20 Hz is used in the following equations to ensure that the re-
sponse is better than 0.5 dB down at 100 Hz.
C
i
≥
1 / (2
π
* 20 k
* 20 Hz) = 0.397 μF; use 0.39 μF.
C
o
≥
1 / (2
π
* 8
* 20 Hz) = 995 μF; use 1000 μF.
The high frequency pole is determined by the product of the
desired high frequency pole, f
, and the closed-loop gain, A
V
. With a closed-loop gain of 1.4 and f
= 100 kHz, the result-
ing GBWP = 140 kHz which is much smaller than the
LM4882 GBWP of 12.5Mhz. This figure displays that if a de-
signer has a need to design an amplifier with a higher gain,
the LM4882 can still be used without running into bandwidth
limitations.
9
www.national.com
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM48820 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Ground-Referenced, Ultra Low Noise, Fixed Gain, 95mW Stereo Headphone Amplifier |
| LM48820TM | 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 |
| LM48820TM/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 |
| LM48820TMBD | 功能描述:BOARD EVAL GROUND REF AUDIO AMP RoHS:否 類別:編程器，開發(fā)系統(tǒng) >> 評估板 - 音頻放大器 系列:Boomer®, PowerWise® 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:1 系列:- |
| LM48820TMBD/NOPB | 功能描述:音頻 IC 開發(fā)工具 LM48820TMBD EVAL BOARD RoHS:否 制造商:Texas Instruments 產(chǎn)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 |
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