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| 型號(hào)： | LM2876MWC |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 40 W, 1 CHANNEL, AUDIO AMPLIFIER, UUC7 |
| 封裝： | WAFER |
| 文件頁(yè)數(shù)： | 5/22頁(yè) |
| 文件大小： | 611K |
| 代理商： | LM2876MWC |
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Application Information (Continued)
Integrated circuits have additional open loop gain allowing
additional feedback loop gain in order to lower harmonic dis-
tortion and improve frequency response. It is this additional
bandwidth that can lead to erroneous signal-to-noise mea-
surements if not considered during the measurement pro-
cess. In the typical example above, the difference in band-
width appears small on a log scale but the factor of 10 in
bandwidth, (200 kHz to 2 MHz) can result in a 10 dB theoreti-
cal difference in the signal-to-noise ratio (white noise is pro-
portional to the square root of the bandwidth in a system).
In comparing audio amplifiers it is necessary to measure the
magnitude of noise in the audible bandwidth by using a
“weighting” filter.(Note 16) A “weighting” filter alters the fre-
quency response in order to compensate for the average hu-
man ear’s sensitivity to the frequency spectra. The weighting
filters at the same time provide the bandwidth limiting as dis-
cussed in the previous paragraph.
Note 16: CCIR/ARM:
A Practical Noise Measurement Method; by Ray
Dolby, David Robinson and Kenneth Gundry, AES Preprint No. 1353 (F-3).
In addition to noise filtering, differing meter types give differ-
ent noise readings. Meter responses include:
1.
RMS reading,
2.
average responding,
3.
peak reading, and
4.
quasi peak reading.
Although theoretical noise analysis is derived using true
RMS based calculations, most actual measurements are
taken with ARM (Average Responding Meter) test equip-
ment.
Typical signal-to-noise figures are listed for an A-weighted fil-
ter which is commonly used in the measurement of noise.
The shape of all weighting filters is similar, with the peak of
the curve usually occurring in the 3 kHz–7 kHz region as
shown below.
SUPPLY BYPASSING
The LM2876 has excellent power supply rejection and does
not require a regulated supply. However, to eliminate pos-
sible oscillations all op amps and power op amps should
have their supply leads bypassed with low-inductance ca-
pacitors having short leads and located close to the package
terminals. Inadequate power supply bypassing will manifest
itself by a low frequency oscillation known as “motorboating”
or by high frequency instabilities. These instabilities can be
eliminated through multiple bypassing utilizing a large tanta-
lum or electrolytic capacitor (10 F or larger) which is used to
absorb low frequency variations and a small ceramic capaci-
tor (0.1 F) to prevent any high frequency feedback through
the power supply lines.
If adequate bypassing is not provided the current in the sup-
ply leads which is a rectified component of the load current
may be fed back into internal circuitry. This signal causes low
distortion at high frequencies requiring that the supplies be
bypassed at the package terminals with an electrolytic ca-
pacitor of 470 F or more.
LEAD INDUCTANCE
Power op amps are sensitive to inductance in the output
lead, particularly with heavy capacitive loading. Feedback to
the input should be taken directly from the output terminal,
minimizing common inductance with the load.
Lead inductance can also cause voltage surges on the sup-
plies. With long leads to the power supply, energy is stored in
the lead inductance when the output is shorted. This energy
can be dumped back into the supply bypass capacitors when
the short is removed. The magnitude of this transient is re-
duced by increasing the size of the bypass capacitor near
the IC. With at least a 20 F local bypass, these voltage
surges are important only if the lead length exceeds a couple
feet (> 1 H lead inductance). Twisting together the supply
and ground leads minimizes the effect.
LAYOUT, GROUND LOOPS AND STABILITY
The LM2876 is designed to be stable when operated at a
closed-loop gain of 10 or greater, but as with any other
high-current amplifier, the LM2876 can be made to oscillate
under certain conditions. These usually involve printed cir-
cuit board layout or output/input coupling.
When designing a layout, it is important to return the load
ground, the output compensation ground, and the low level
(feedback and input) grounds to the circuit board common
ground point through separate paths. Otherwise, large cur-
rents flowing along a ground conductor will generate volt-
ages on the conductor which can effectively act as signals at
the input, resulting in high frequency oscillation or excessive
distortion. It is advisable to keep the output compensation
components and the 0.1 F supply decoupling capacitors as
close as possible to the LM2876 to reduce the effects of PCB
trace resistance and inductance. For the same reason, the
ground return paths should be as short as possible.
In general, with fast, high-current circuitry, all sorts of prob-
lems can arise from improper grounding which again can be
avoided by returning all grounds separately to a common
point. Without isolating the ground signals and returning the
grounds to a common point, ground loops may occur.
“Ground Loop” is the term used to describe situations occur-
ring in ground systems where a difference in potential exists
between two ground points. Ideally a ground is a ground, but
unfortunately, in order for this to be true, ground conductors
with zero resistance are necessary. Since real world ground
DS011775-13
DS011775-14
LM2876
www.national.com
13
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM2876T | 制造商:Texas Instruments 功能描述:AMP AUDIO + MUTE 75W 2876 SIL-11 |
| LM2876T | 制造商:Texas Instruments 功能描述:AMP AUDIO + MUTE 75W 2876 SIL-11 |
| LM2876T/NOPB | 功能描述:IC AMP AUDIO PWR 40W 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) |
| LM2876TF | 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 |
| LM2876TF NOPB | 制造商:Texas Instruments 功能描述:Audio Amp Speaker 1-CH Mono 40W Class-AB 11-Pin(11+Tab) TO-220 Rail |
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