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參數(shù)資料
| 型號： | LM4809 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Dual 105mW Headphone Amplifier with Active-Low Shutdown Mode |
| 中文描述： | 雙105mW耳機放大器的有源低關斷模式 |
| 文件頁數(shù)： | 13/18頁 |
| 文件大小： | 903K |
| 代理商： | LM4809 |
Application Information
(Continued)
find the minimum supply voltage is to use the Output Power
vs Supply Voltage curve in the
Typical Performance Char-
acteristics
section. Another way, using Equation (5), is to
calculate the peak output voltage necessary to achieve the
desired output power for a given load impedance. To ac-
count for the amplifier’s dropout voltage, two additional volt-
ages, based on the Dropout Voltage vs Supply Voltage in the
Typical Performance Characteristics
curves, must be
added to the result obtained by Equation (5). For a
single-ended application, the result is Equation (6).
(5)
V
DD
≥
(2V
OPEAK
+ (V
OD
TOP
+ V
OD
BOT
))
(6)
The Output Power vs Supply Voltage graph for a 32
load
indicates a minimum supply voltage of 4.8V. This is easily
met by the commonly used 5V supply voltage. The additional
voltage creates the benefit of headroom, allowing the
LM4809 to produce peak output power in excess of 70mW
without clipping or other audible distortion. The choice of
supply voltage must also not create a situation that violates
maximum power dissipation as explained above in the
Power Dissipation
section. Remember that the maximum
power dissipation point 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 Equa-
tion (7).
(7)
Thus, a minimum gain of 1.497 allows the LM4809 to reach
full output swing and maintain low noise and THD+N perfro-
mance. For this example, let A
V
=1.5.
The amplifiers overall gain is set using the input (R
i
) and
feedback (R
f
) resistors. With the desired input impedance
set at 20k
, the feedback resistor is found using Equation
(8).
A
V
= R
f
/R
i
(8)
The value of R
f
is 30k
.
The last step in this design is setting the amplifier’s 3db
frequency bandwidth. To achieve the desired
±
0.25dB pass
band magnitude variation limit, the low frequency response
must extend to at lease onefifth the lower bandwidth limit
and the high frequency response must extend to at least five
times the upper bandwidth limit. The gain variation for both
response limits is 0.17dB, well within the
±
0.25dB desired
limit. The results are an
f
L
= 100Hz/5 = 20Hz
(9)
and a
f
H
= 20kHz
*
5 = 100kHz
(10)
As stated in the
External Components
section, both R
in
conjunction with C
, and C
with R
, create first order high-
pass filters. Thus to obtain the desired low frequency re-
sponse of 100Hz within
±
0.5dB, 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 0.34dB at five times away
from the single order filter 3dB point. Thus, a frequency of
20Hz is used in the following equations to ensure that the
response is better than 0.5dB down at 100Hz.
C
i
≥
1 / (2
π
* 20k
* 20Hz) = 0.397μF; use 0.39μF.(11)
C
o
≥
1 / (2
π
* 32
* 20Hz) = 249μF; use 330μF. (12)
The high frequency pole is determined by the product of the
desired high frequency pole, f
H
, and the closed-loop gain,
A
V
. With a closed-loop gain of 1.5 and f
H
= 100kHz, the
resulting GBWP = 150kHz which is much smaller than the
LM4809’s GBWP of 900kHz. This figure displays that if a
designer has a need to design an amplifier with a higher
gain, the LM4809 can still be used without running into
bandwidth limitations.
L
www.national.com
13
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LM4809LD | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Dual 105mW Headphone Amplifier with Active-Low Shutdown Mode |
| LM4809LD/NOPB | 功能描述:IC AMP AUDIO PWR .105W STER 8LLP RoHS:是 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:Boomer® 產(chǎn)品培訓模塊: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 供應商設備封裝:25-WLP（2.09x2.09） 封裝/外殼:25-WFBGA，WLCSP 包裝:帶卷 (TR) |
| LM4809LDBD | 功能描述:BOARD EVALUATION LM4809LD RoHS:否 類別:編程器，開發(fā)系統(tǒng) >> 評估板 - 音頻放大器 系列:Boomer® 產(chǎn)品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:1 系列:- |
| LM4809LDX | 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 |
| LM4809LDX/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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