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參數(shù)資料
| 型號(hào)： | LM4861MWA |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類(lèi)： | 音頻／視頻放大 |
| 英文描述： | 1.1 W, 1 CHANNEL, AUDIO AMPLIFIER, UUC |
| 封裝： | WAFER |
| 文件頁(yè)數(shù)： | 9/11頁(yè) |
| 文件大?。?/td> | 273K |
| 代理商： | LM4861MWA |
Application Information (Continued)
tion of R
f and Cf will cause rolloff before 20 kHz. A typical
combination of feedback resistor and capacitor that will not
produce audio band high frequency rolloff is R
f = 100 k and
C
f = 5 pF. These components result in a 3 dB point of ap-
proximately 320 kHz. Once the differential gain of the ampli-
fier has been calculated, a choice of R
f will result, and Cf can
then be calculated from the formula stated in the External
Components Description section.
VOICE-BAND AUDIO AMPLIFIER
Many applications, such as telephony, only require a voice-
band frequency response. Such an application usually re-
quires a flat frequency response from 300 Hz to 3.5 kHz. By
adjusting the component values of
Figure 2, this common
application requirement can be implemented. The combina-
tion of R
i and Ci form a highpass filter while Rf and Cf form a
lowpass filter. Using the typical voice-band frequency range,
with a passband differential gain of approximately 100, the
following values of R
i,Ci,Rf, and Cf follow from the equa-
tions stated in the External Components Description sec-
tion.
R
i =10k,Rf = 510k ,Ci = 0.22 F, and Cf =15pF
Five times away from a 3 dB point is 0.17 dB down from the
flatband response. With this selection of components, the re-
sulting 3 dB points, f
L and fH, are 72 Hz and 20 kHz, re-
spectively, resulting in a flatband frequency response of bet-
ter than ±0.25 dB with a rolloff of 6 dB/octave outside of the
passband. If a steeper rolloff is required, other common
bandpass filtering techniques can be used to achieve higher
order filters.
SINGLE-ENDED AUDIO AMPLIFIER
Although the typical application for the LM4861 is a bridged
monoaural amp, it can also be used to drive a load single-
endedly in applications, such as PC cards, which require that
one side of the load is tied to ground.
Figure 3 shows a com-
mon single-ended application, where V
O1 is used to drive the
speaker. This output is coupled through a 470 F capacitor,
which blocks the half-supply DC bias that exists in all single-
supply amplifier configurations. This capacitor, designated
C
O in Figure 3, in conjunction with RL, forms a highpass filter.
The 3 dB point of this high pass filter is 1/(2
πR
LCO), so care
should be taken to make sure that the product of R
L and CO
is large enough to pass low frequencies to the load. When
driving an 8
load, and if a full audio spectrum reproduction
is required, C
O should be at least 470 F. VO2, the output
that is not used, is connected through a 0.1 F capacitor to
a2k
load to prevent instability. While such an instability will
not affect the waveform of V
O1, it is good design practice to
load the second output.
AUDIO POWER AMPLIFIER DESIGN
Design a 1W / 8
Audio Amplifier
Given:
Power Output
1 Wrms
Load Impedance
8
Input Level
1 Vrms
Input Impedance
20 k
Bandwidth
100 Hz–20 kHz ± 0.25 dB
A designer must first determine the needed supply rail to ob-
tain the specified output power. By extrapolating from the
Output Power vs Supply Voltage graph in the Typical Per-
formance Characteristics section, the supply rail can be
easily found. A second way to determine the minimum sup-
ply rail is to calculate the required V
opeak using Equation 3
and add the dropout voltage. Using this method, the mini-
mum supply voltage would be (V
opeak +VOD , where VOD is
typically 0.6V.
(3)
For 1W of output power into an 8
load, the required V
opeak
is 4.0V. A minumum supply rail of 4.6V results from adding
V
opeak and Vod. But 4.6V is not a standard voltage that exists
in many applications and for this reason, a supply rail of 5V
is designated. Extra supply voltage creates dynamic head-
room that allows the LM4861 to reproduce peaks in excess
of 1Wwithout 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.
Once the power dissipation equations have been addressed,
the required differential gain can be determined from Equa-
tion 4.
(4)
R
f/Ri =AVD/2
(5)
From equation 4, the minimum A
vd is 2.83: Avd =3
Since the desired input impedance was 20 k
, and with a
A
vd of 3, a ratio of 1:1.5 of Rf to Ri results in an allocation of
R
i =20k,Rf =30k. The final design step is to address
the bandwidth requirements which must be stated as a pair
of 3 dB frequency points. Five times away from a 3 db
point is 0.17 dB down from passband response which is bet-
ter than the required ±0.25 dB specified. This fact results in
a low and high frequency pole of 20 Hz and 100 kHz respec-
tively. As stated in the External Components section, R
i in
conjunction with C
i create a highpass filter.
C
i ≥ 1/(2π*20 k*20 Hz) = 0.397 F; use 0.39 F.
The high frequency pole is determined by the product of the
desired high frequency pole, f
H, and the differential gain, Avd.
With a A
vd = 2 and fH = 100 kHz, the resulting GBWP =
100 kHz which is much smaller than the LM4861 GBWP of
4 MHz. This figure displays that if a designer has a need to
design an amplifier with a higher differential gain, the
LM4861 can still be used without running into bandwidth
problems.
LM4861
www.national.com
7
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM4861MX | 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(lèi)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 |
| LM4861MX/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(lèi)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 |
| LM4861MX-NOPB | 制造商:TI 制造商全稱(chēng):Texas Instruments 功能描述:LM4861 1.1W Audio Power Amplifier with Shutdown Mode |
| LM4862 | 制造商:UTC-IC 制造商全稱(chēng):UTC-IC 功能描述:AUDIO POWER AMPLIFIER WITH SHUTDOWN MODE |
| LM4862G-D08-T | 制造商:UTC-IC 制造商全稱(chēng):UTC-IC 功能描述:AUDIO POWER AMPLIFIER WITH SHUTDOWN MODE |
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