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| 型號： | LM4855LQ/NOPB |
| 廠商： | National Semiconductor |
| 文件頁數(shù)： | 10/27頁 |
| 文件大?。?/td> | 0K |
| 描述： | IC AMP AUDIO PWR 1.5W MONO 24LLP |
| 標準包裝： | 1 |
| 系列： | Boomer® |
| 類型： | AB 類 |
| 輸出類型： | 1-通道（單聲道），帶立體聲耳機 |
| 在某負載時最大輸出功率 x 通道數(shù)量： | 1.5W x 1 @ 4 歐姆; 115mW x 2 @ 32 歐姆 |
| 電源電壓： | 2.6 V ~ 5 V |
| 特點： | 消除爆音，靜音，關機，SPI，熱保護，音量控制 |
| 安裝類型： | 表面貼裝 |
| 供應商設備封裝： | 24-LLP-EP（4x5） |
| 封裝/外殼： | 24-WFQFN 裸露焊盤 |
| 包裝： | 標準包裝 |
| 配用： | LM4855LQBD-ND - BOARD EVALUATION LM4855LQ |
| 其它名稱： | LM4855LQDKR |
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SNAS164C – JUNE 2002 – REVISED MAY 2013
Bridge mode amplifiers are different from single-ended amplifiers that drive loads connected between a single
amplifier's output and ground. For a given supply voltage, bridge mode has a distinct advantage over the single-
ended configuration: its differential output doubles the voltage swing across the load. Theoretically, this produces
four times the output power when compared to a single-ended amplifier under the same conditions. This increase
in attainable output power assumes that the amplifier is not current limited and that the output signal is not
clipped.
Another advantage of the differential bridge output is no net DC voltage across the load. This is accomplished by
biasing SPKROUT- and SPKROUT+ outputs at half-supply. This eliminates the coupling capacitor that single
supply, single-ended amplifiers require. Eliminating an output coupling capacitor in a typical single-ended
configuration forces a single-supply amplifier's half-supply bias voltage across the load. This increases internal IC
power dissipation and may permanently damage loads such as speakers.
POWER DISSIPATION
Power dissipation is a major concern when designing a successful single-ended or bridged amplifier.
A direct consequence of the increased power delivered to the load by a bridge amplifier is higher internal power
dissipation. The LM4855 has a pair of bridged-tied amplifiers driving a handsfree speaker, SPKROUT. The
maximum internal power dissipation operating in the bridge mode is twice that of a single-ended amplifier. From
Equation (2), assuming a 5V power supply and an 8
load, the maximum SPKROUT power dissipation is
634mW.
PDMAX-SPKROUT = 4(VDD)
2/(2π2 R
L): Bridge Mode
(2)
The LM4855 also has 2 pairs of bridged-tied amplifiers driving stereo headphones, ROUT and LOUT. The
maximum internal power dissipation for ROUT and LOUT is given by equation (3) and (4). From Equations (3)
and (4), assuming a 5V power supply and a 32
load, the maximum power dissipation for LOUT and ROUT is
158mW, or 316mW total.
PDMAX-LOUT = 4(VDD)
2/(2π2 R
L): Bridge Mode
(3)
PDMAX-ROUT = 4(VDD)
2/(2π2 R
L): Bridge Mode
(4)
The maximum internal power dissipation of the LM4855 occurs when all 3 amplifiers pairs are simultaneously on;
and is given by Equation (5).
PDMAX-TOTAL = PDMAX-SPKROUT + PDMAX-LOUT + PDMAX-ROUT
(5)
The maximum power dissipation point given by Equation (5) must not exceed the power dissipation given by
Equation (6):
PDMAX' = (TJMAX - TA)/ θJA
(6)
The LM4855's TJMAX = 150°C. In the YZR package, the LM4855's
θJA is 48°C/W. In the NHW package soldered
to a DAP pad that expands to a copper area of 2.5in2 on a PCB, the LM4855's
θJA is 42°C/W. At any given
ambient temperature TA, use Equation (6) to find the maximum internal power dissipation supported by the IC
packaging. Rearranging Equation (6) and substituting PDMAX-TOTAL for PDMAX' results in Equation (7). This
equation gives the maximum ambient temperature that still allows maximum stereo power dissipation without
violating the LM4855's maximum junction temperature.
TA = TJMAX - PDMAX-TOTALθJA
(7)
For a typical application with a 5V power supply and an 8
load, the maximum ambient temperature that allows
maximum stereo power dissipation without exceeding the maximum junction temperature is approximately 104°C
for the YZR package.
TJMAX = PDMAX-TOTAL θJA + TA
(8)
Equation (8) gives the maximum junction temperature TJMAX. If the result violates the LM4855's 150°C, reduce
the maximum junction temperature by reducing the power supply voltage or increasing the load resistance.
Further allowance should be made for increased ambient temperatures.
The above examples assume that a device is a surface mount part operating around the maximum power
dissipation point. Since internal power dissipation is a function of output power, higher ambient temperatures are
allowed as output power or duty cycle decreases. If the result of Equation (5) is greater than that of Equation (6),
then decrease the supply voltage, increase the load impedance, or reduce the ambient temperature. If these
measures are insufficient, a heat sink can be added to reduce
θJA. The heat sink can be created using additional
18
Copyright 2002–2013, Texas Instruments Incorporated
Product Folder Links: LM4855
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LM4855LQX/NOPB | 制造商:Texas Instruments 功能描述:Audio Amp Headphone/Speaker 1-CH Mono/2-CH Stereo 1.5W Class-AB 24-Pin LLP EP T/R |
| LM4856 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Integrated Audio Amplifier System |
| LM48560 | 制造商:TI 制造商全稱:Texas Instruments 功能描述:High Voltage Class H Ceramic Speaker Driver with Automatic Level Control |
| LM48560TL | 制造商:TI 制造商全稱:Texas Instruments 功能描述:High Voltage Class H Ceramic Speaker Driver with Automatic Level Control |
| LM48560TL/NOPB | 功能描述:音頻放大器 Hi Vltg Class H Cer Speaker Driver RoHS:否 制造商:STMicroelectronics 產品: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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