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參數(shù)資料
| 型號： | LM3875DWF |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 56 W, 1 CHANNEL, AUDIO AMPLIFIER, UUC |
| 封裝： | WAFER |
| 文件頁數(shù)： | 6/23頁 |
| 文件大小： | 600K |
| 代理商： | LM3875DWF |
Application Information (Continued)
The load current I
L will be much larger than input bias current
I
1, thus V1 will follow the output voltage directly, i.e., in
phase. Therefore the voltage appearing at the non-inverting
input is effectively positive feedback and the circuit may os-
cillate. If there were only one device to worry about then the
values of R
1 and R2 would probably be small enough to be
ignored; however, several devices normally comprise a total
system. Any ground return of a separate device, whose out-
put is in phase, can feedback in a similar manner and cause
instabilities. Out of phase ground loops also are trouble-
some, causing unexpected gain and phase errors.
The solution to most ground loop problems is to always use
a single-point ground system, although this is sometimes im-
practical. The third figure above is an example of a
single-point ground system.
The single-point ground concept should be applied rigor-
ously to all components and all circuits when possible. Viola-
tions of single-point grounding are most common among
printed circuit board designs, since the circuit is surrounded
by large ground areas which invite the temptation to run a
device to the closest ground spot. As a final rule, make all
ground returns low resistance and low inductance by using
large wire and wide traces.
Occasionally, current in the output leads (which function as
antennas) can be coupled through the air to the amplifier in-
put, resulting in high-frequency oscillation. This normally
happens when the source impedance is high or the input
leads are long. The problem can be eliminated by placing a
small capacitor, C
C, (on the order of 50 pF– 500 pF) across
the LM3875 input terminals. Refer to the External Compo-
nents Description section relating to component interaction
with C
f.
REACTIVE LOADING
It is hard for most power amplifiers to drive highly capacitive
loads very effectively and normally results in oscillations or
ringing on the square wave response. If the output of the
LM3875 is connected directly to a capacitor with no series
resistance, the square wave response will exhibit ringing if
the capacitance is greater than about 0.2 F. If highly capaci-
tive loads are expected due to long speaker cables, a
method commonly employed to protect amplifiers from low
impedances at high frequencies is to couple to the load
through a 10
resistor in parallel with a 0.7 H inductor. The
inductor-resistor combination as shown in the Typical Appli-
cation Circuit isolates the feedback amplifier from the load
by providing high output impedance at high frequencies thus
allowing the 10
resistor to decouple the capacitive load and
reduce the Q of the series resonant circuit. The LR combina-
tion also provides low output impedance at low frequencies
thus shorting out the 10
resistor and allowing the amplifier
to drive the series RC load (large capacitive load due to long
speaker cables) directly.
GENERALIZED AUDIO POWER AMPLIFIER DESIGN
The system designer usually knows some of the following
parameters when starting an audio amplifier design:
Desired Power Output
Input Level
Input Impedance
Load Impedance
Maximum Supply Voltage
Bandwidth
The power output and load impedance determine the power
supply requirements, however, depending upon the applica-
tion some system designers may be limited to certain maxi-
mum supply voltages. If the designer does have a power
supply limitation, he should choose a practical load imped-
ance which would allow the amplifier to provide the desired
output power, keeping in mind the current limiting capabili-
ties of the device. In any case, the output signal swing and
current are found from (where P
O is the average output
power):
(5)
(6)
To determine the maximum supply voltage the following pa-
rameters must be considered. Add the dropout voltage
(5 volts for LM3875) to the peak output swing, V
opeak,toget
the supply rail value, (i.e. + V
opeak + Vod) at a current of
I
opeak). The regulation of the supply determines the unloaded
voltage, usually about 15% higher. Supply voltage will also
rise 10% during high line conditions. Therefore, the maxi-
mum supply voltage is obtained from the following equation:
max. supplies
≈ ± (V
opeak + Vod(1 + regulation)(1.1) (7)
The input sensitivity and the output power specs determine
the minimum required gain as depicted below:
(8)
Normally the gain is set between 20 and 200; for a 40W, 8
audio amplifier this results in a sensitivity of 894 mV and
89 mV, respectively. Although higher gain amplifiers provide
greater output power and dynamic headroom capabilities,
there are certain shortcomings that go along with the so
called “gain”. The input referred noise floor is increased and
hence the SNR is worse. With the increase in gain, there is
also a reduction of the power bandwidth which results in a
DS011449-13
www.national.com
14
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM3875T | 功能描述:IC AMP AUDIO PWR 56W AB TO220-11 RoHS:是 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:Overture™ 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:2,500 系列:DirectDrive® 類型:H 類 輸出類型:耳機(jī)，2-通道（立體聲） 在某負(fù)載時(shí)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(diǎn):I²C，麥克風(fēng)，靜音，短路保護(hù)，音量控制 安裝類型:表面貼裝 供應(yīng)商設(shè)備封裝:25-WLP（2.09x2.09） 封裝/外殼:25-WFBGA，WLCSP 包裝:帶卷 (TR) |
| LM3875T | 制造商:Texas Instruments 功能描述:IC AMP AUDIO 100W 3875 SIL-11 |
| LM3875T/NOPB | 制造商:Texas Instruments 功能描述:Audio Amp Speaker 1-CH Mono 56W Class-AB 11-Pin(11+Tab) TO-220 |
| LM3875TF | 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 |
| LM3875TF/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 |
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