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參數(shù)資料
| 型號： | LM4856ITL/NOPB |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 1.1 W, 3 CHANNEL, AUDIO AMPLIFIER, PBGA18 |
| 封裝： | MICRO SMD-18 |
| 文件頁數(shù)： | 9/23頁 |
| 文件大?。?/td> | 1321K |
| 代理商： | LM4856ITL/NOPB |
Application Information (Continued)
not placed on the same PCB layer as the LM4856 should be
5in
2 (min) for the same supply voltage and load resistance.
The last two area recommendations apply for 25C ambient
temperature. Increase the area to compensate for ambient
temperatures above 25C. In all circumstances and under all
conditions, the junction temperature must be held below
150C to prevent activating the LM4856’s thermal shutdown
protection. Further detailed and specific information con-
cerning PCB layout and fabrication and mounting an LD
(LLP) is found in National Semiconductor’s AN1187.
PCB LAYOUT AND SUPPLY REGULATION
CONSIDERATIONS FOR DRIVING 3
AND 4 LOADS
Power dissipated by a load is a function of the voltage swing
across the load and the load’s impedance. As load imped-
ance decreases, load dissipation becomes increasingly de-
pendent on the interconnect (PCB trace and wire) resistance
between the amplifier output pins and the load’s connec-
tions. Residual trace resistance causes a voltage drop,
which results in power dissipated in the trace and not in the
load as desired. For example, 0.1
trace resistance reduces
the output power dissipated by a 4
load from 1.7W to 1.6W.
The problem of decreased load dissipation is exacerbated
as load impedance decreases. Therefore, to maintain the
highest load dissipation and widest output voltage swing,
PCB traces that connect the output pins to a load must be as
wide as possible.
Poor power supply regulation adversely affects maximum
output power. A poorly regulated supply’s output voltage
decreases with increasing load current. Reduced supply
voltage causes decreased headroom, output signal clipping,
and reduced output power. Even with tightly regulated sup-
plies, trace resistance creates the same effects as poor
supply regulation. Therefore, making the power supply
traces as wide as possible helps maintain full output voltage
swing.
BRIDGE CONFIGURATION EXPLANATION
As shown in Figure 1, the LM4856 consists of three pairs of
output amplifier blocks (A4-A6). Amplifier block A6 consists
of a bridged-tied amplifier pair that drives SPKROUT. The
LM4856 drives a load, such as a speaker, connected be-
tween outputs, SPKROUT+ and SPKROUT-. In the amplifier
block A6, the output of the amplifier that drives SPKROUT-
serves as the input to the unity gain inverting amplifier that
drives SPKROUT+.
This results in both amplifiers producing signals identical in
magnitude, but 180 out of phase. Taking advantage of this
phase difference, a load is placed between SPKROUT- and
SPKROUT+ and driven differentially (commonly referred to
as ’bridge mode’). This results in a differential or BTL gain of:
A
VD = 2(Rf /Ri)=2
(1)
Bridge mode amplifiers are different from single-ended am-
plifiers that drive loads connected between a single amplifi-
er’s output and ground. For a given supply voltage, bridge
mode has a distinct advantage over the single-ended con-
figuration: 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 ca-
pacitor 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 dissi-
pation. The LM4856 has a pair of bridged-tied amplifiers
driving a handsfree speaker, SPKROUT. The maximum in-
ternal 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.
P
DMAX-SPKROUT = 4(VDD)
2 / (2
π2 R
L): Bridge Mode
(2)
The LM4856 also has a pair of single-ended amplifiers driv-
ing 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 40mW, or 80mW total.
P
DMAX-LOUT =(VDD)
2 /(2
π2 R
L): Single-ended Mode (3)
P
DMAX-ROUT =(VDD)
2 /(2
π2 R
L): Single-ended Mode (4)
The maximum internal power dissipation of the LM4856
occurs when all 3 amplifiers pairs are simultaneously on; and
is given by Equation (5).
P
DMAX-TOTAL =
P
DMAX-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):
P
DMAX’= (TJMAX -TA)/
θ
JA
(6)
The LM4856’s T
JMAX = 150C. In the ITL package, the
LM4856’s
θ
JA is 48C/W. In the LD package soldered to a
DAP pad that expands to a copper area of 2.5in
2 on a PCB,
the LM4856’s
θ
JA is 42C/W. At any given ambient tempera-
ture T
A, use Equation (6) to find the maximum internal power
dissipation supported by the IC packaging. Rearranging
Equation (6) and substituting P
DMAX-TOTAL for PDMAX’ results
in Equation (7). This equation gives the maximum ambient
LM4856
www.national.com
17
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM4856LQ | 制造商:Texas Instruments 功能描述:1W MONO 100MW STEREO SUBSYST 4856 |
| LM4856LQ/NOPB | 功能描述:IC AMP AUDIO PWR 1.5W MONO 24LLP RoHS:是 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:Boomer® 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，2-通道（立體聲） 在某負(fù)載時最大輸出功率 x 通道數(shù)量:35mW x 2 @ 16 歐姆 電源電壓:1.62 V ~ 1.98 V 特點:I²C，麥克風(fēng)，靜音，短路保護，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) |
| LM4856LQBD | 功能描述:BOARD EVALUATION LM4856LQ RoHS:否 類別:編程器，開發(fā)系統(tǒng) >> 評估板 - 音頻放大器 系列:Boomer® 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:1 系列:- |
| LM4857 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Stereo 1.2W Audio Sub-system with 3D Enhancement |
| LM4857_05 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Stereo 1.2W Audio Sub-system with 3D Enhancement |
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