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參數(shù)資料
| 型號： | LM4671ITLX/NOPB |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 2.5 W, 1 CHANNEL, AUDIO AMPLIFIER, PBGA9 |
| 封裝： | MICRO, SMD-9 |
| 文件頁數(shù)： | 10/10頁 |
| 文件大?。?/td> | 589K |
| 代理商： | LM4671ITLX/NOPB |
Shutdown Current vs Supply Voltage
R
L = 15μH+8+15μH
20107321
Application Information
GENERAL AMPLIFIER FUNCTION
The LM4671 features a filterless modulation scheme. The
differential outputs of the device switch at 300kHz from V
DD
to GND. When there is no input signal applied, the two outputs
(V
O1 and VO2) switch with a 50% duty cycle, with both outputs
in phase. Because the outputs of the LM4671 are differential,
the two signals cancel each other. This results in no net volt-
age across the speaker, thus there is no load current during
an idle state, conserving power.
With an input signal applied, the duty cycle (pulse width) of
the LM4671 outputs changes. For increasing output voltages,
the duty cycle of V
O1 increases, while the duty cycle of VO2
decreases. For decreasing output voltages, the converse oc-
curs, the duty cycle of V
O2 increases while the duty cycle of
V
O1 decreases. The difference between the two pulse widths
yields the differential output voltage.
POWER DISSIPATION AND EFFICIENCY
In general terms, efficiency is considered to be the ratio of
useful work output divided by the total energy required to pro-
duce it with the difference being the power dissipated, typi-
cally, in the IC. The key here is “useful” work. For audio
systems, the energy delivered in the audible bands is con-
sidered useful including the distortion products of the input
signal.
Sub-sonic
(DC)
and
super-sonic
components
(>22kHz) are not useful. The difference between the power
flowing from the power supply and the audio band power be-
ing transduced is dissipated in the LM4671 and in the trans-
ducer load. The amount of power dissipation in the LM4671
is very low. This is because the ON resistance of the switches
used to form the output waveforms is typically less than
0.25
. This leaves only the transducer load as a potential
"sink" for the small excess of input power over audio band
output power. The LM4671 dissipates only a fraction of the
excess power requiring no additional PCB area or copper
plane to act as a heat sink.
DIFFERENTIAL AMPLIFIER EXPLANATION
As logic supply voltages continue to shrink, designers are in-
creasingly turning to differential analog signal handling to
preserve signal to noise ratios with restricted voltage swing.
The LM4671 is a fully differential amplifier that features dif-
ferential input and output stages. A differential amplifier am-
plifies the difference between the two input signals. Tradition-
al audio power amplifiers have typically offered only single-
ended inputs resulting in a 6dB reduction in signal to noise
ratio relative to differential inputs. The LM4671 also offers the
possibility of DC input coupling which eliminates the two ex-
ternal AC coupling, DC blocking capacitors. The LM4671 can
be used, however, as a single ended input amplifier while still
retaining it's fully differential benefits. In fact, completely un-
related signals may be placed on the input pins. The LM4671
simply amplifies the difference between the signals. A major
benefit of a differential amplifier is the improved common
mode rejection ratio (CMRR) over single input amplifiers. The
common-mode rejection characteristic of the differential am-
plifier reduces sensitivity to ground offset related noise injec-
tion, especially important in high noise applications.
PCB LAYOUT CONSIDERATIONS
As output power increases, interconnect resistance (PCB
traces and wires) between the amplifier, load and power sup-
ply create a voltage drop. The voltage loss on the traces
between the LM4671 and the load results is lower output
power and decreased efficiency. Higher trace resistance be-
tween the supply and the LM4671 has the same effect as a
poorly regulated supply, increase ripple on the supply line al-
so reducing the peak output power. The effects of residual
trace resistance increases as output current increases due to
higher output power, decreased load impedance or both. To
maintain the highest output voltage swing and corresponding
peak output power, the PCB traces that connect the output
pins to the load and the supply pins to the power supply
should be as wide as possible to minimize trace resistance.
The use of power and ground planes will give the best THD
+N performance. While reducing trace resistance, the use of
power planes also creates parasite capacitors that help to fil-
ter the power supply line.
The inductive nature of the transducer load can also result in
overshoot on one or both edges, clamped by the parasitic
diodes to GND and V
DD in each case. From an EMI stand-
point, this is an aggressive waveform that can radiate or
conduct to other components in the system and cause inter-
9
www.national.com
LM4671
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LM4673 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Filterless, 2.65W, Mono, Class D Audio Power Amplifier |
| LM4673_07 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Filterless, 2.65W, Mono, Class D Audio Power Amplifier |
| LM4673SD | 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 |
| LM4673SD/NOPB | 功能描述:音頻放大器 FILTERLES,2.65W,MONO CLASS D AUD PWR AMP 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 |
| LM4673SDBD | 功能描述:音頻 IC 開發(fā)工具 LM4673SD 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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