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參數資料
| 型號： | LM4849MH |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻控制 |
| 英文描述： | Stereo 2W Audio Power Amplifiers with DC Volume Control and Input Mux |
| 中文描述： | 2 CHANNEL(S), VOLUME CONTROL CIRCUIT, PDSO28 |
| 封裝： | TSSOP-28 |
| 文件頁數： | 13/19頁 |
| 文件大小： | 690K |
| 代理商： | LM4849MH |
Application Information
EXPOSED-DAP MOUNTING CONSIDERATIONS
The LM4849’s exposed-DAP (die attach paddle) package
(MH) provides a low thermal resistance between the die and
the PCB to which the part is mounted and soldered. This
allows rapid heat transfer from the die to the surrounding
PCB copper traces, ground plane and, finally, surrounding
air. The result is a low voltage audio power amplifier that
produces 2.1W at
≤
1% THD with a 4
load. This high power
is achieved through careful consideration of necessary ther-
mal design. Failing to optimize thermal design may compro-
mise the LM4849’s high power performance and activate
unwanted, though necessary, thermal shutdown protection.
The MH package must have its exposed DAP soldered to a
grounded copper pad on the PCB. The DAP’s PCB copper
pad is connected to a large plane of continuous unbroken
copper. This plane forms a thermal mass and heat sink and
radiation area. Place the heat sink area on either outside
plane in the case of a two-sided PCB, or on an inner layer of
a board with more than two layers. Connect the DAP copper
pad to the inner layer or backside copper heat sink area with
32(4x8)
(MH)
vias.
The
0.012in–0.013in with a 1.27mm pitch. Ensure efficient ther-
mal conductivity by plating-through and solder-filling the
vias.
Best thermal performance is achieved with the largest prac-
tical copper heat sink area. If the heatsink and amplifier
share the same PCB layer, a nominal 2.5in
2
(min) area is
necessary for 5V operation with a 4
load. Heatsink areas
not placed on the same PCB layer as the LM4849 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 systems using cooling fans, the
LM4849MH can take advantage of forced air cooling. With
an air flow rate of 450 linear-feet per minute and a 2.5in
2
exposed copper or 5.0in
2
inner layer copper plane heatsink,
the LM4849MH can continuously drive a 3
load to full
power. The LM4849’s power de-rating curve in the
Typical
Performance Characteristics
shows the maximum power
dissipation versus temperature. Example PCB layouts for
the exposed-DAP TSSOP package is shown in the
Demon-
stration Board Layout
section.
via
diameter
should
be
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 2.1W to 2.0W.
This 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 LM4849 output stage consists of
two pairs of operational amplifiers, forming a two-channel
(channel A and channel B) stereo amplifier. (Though the
following discusses channel A, it applies equally to channel
B.)
Figure 1
shows that the first amplifier’s negative (-) output
serves as the second amplifier’s input. 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 OUTA and +OUTA and driven dif-
ferentially (commonly referred to as “bridge mode”). This
results in a differential gain of
A
VD
= 2 * (R
f
/R
i
)
(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.
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 or that the
output signal is not clipped. To ensure minimum output sig-
nal clipping when choosing an amplifier’s closed-loop gain,
refer to the
Audio Power Amplifier Design
section.
Another advantage of the differential bridge output is no net
DC voltage across the load. This is accomplished by biasing
channel A’s and channel B’s outputs at half-supply. This
eliminates the coupling capacitor that single supply, single-
ended amplifiers require. Eliminating an output coupling ca-
pacitor in a single-ended configuration forces a single-supply
amplifier’s half-supply bias voltage across the load. This
increases internal IC power dissipation and may perma-
nently damage loads such as speakers.
POWER DISSIPATION
Power dissipation is a major concern when designing a
successful single-ended or bridged amplifier. Equation (2)
states the maximum power dissipation point for a single-
ended amplifier operating at a given supply voltage and
driving a specified output load.
P
DMAX
= (V
DD
)
2
/(2
π
2
R
L
)
Single-Ended
(2)
However, a direct consequence of the increased power de-
livered to the load by a bridge amplifier is higher internal
power dissipation for the same conditions.
The LM4849 has two operational amplifiers per channel. The
maximum internal power dissipation per channel operating in
the bridge mode is four times that of a single-ended ampli-
fier. From Equation (3), assuming a 5V power supply and a
4
load, the maximum single channel power dissipation is
1.27W or 2.54W for stereo operation.
P
DMAX
= 4 * (V
DD
)
2
/(2
π
2
R
L
)
Bridge Mode
(3)
L
www.national.com
13
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相關代理商/技術參數 |
參數描述 |
|---|---|
| LM4849MH/NOPB | 功能描述:IC AMP AUDIO PWR 2.2W AB 28TSSOP RoHS:是 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:Boomer® 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:2,500 系列:DirectDrive® 類型:H 類 輸出類型:耳機，2-通道（立體聲） 在某負載時最大輸出功率 x 通道數量:35mW x 2 @ 16 歐姆 電源電壓:1.62 V ~ 1.98 V 特點:I²C，麥克風，靜音，短路保護，音量控制 安裝類型:表面貼裝 供應商設備封裝:25-WLP（2.09x2.09） 封裝/外殼:25-WFBGA，WLCSP 包裝:帶卷 (TR) |
| LM4849MHX/NOPB | 功能描述:IC AMP AUDIO PWR 2.2W AB 28TSSOP RoHS:是 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:Boomer® 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:2,500 系列:DirectDrive® 類型:H 類 輸出類型:耳機，2-通道（立體聲） 在某負載時最大輸出功率 x 通道數量:35mW x 2 @ 16 歐姆 電源電壓:1.62 V ~ 1.98 V 特點:I²C，麥克風，靜音，短路保護，音量控制 安裝類型:表面貼裝 供應商設備封裝:25-WLP（2.09x2.09） 封裝/外殼:25-WFBGA，WLCSP 包裝:帶卷 (TR) |
| LM4850 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Mono 1.5 W / Stereo 300 mW Power Amplifier |
| LM4850A E WAF | 制造商:Texas Instruments 功能描述: |
| LM4850LD | 制造商:Rochester Electronics LLC 功能描述:1.5W MON AUD&95MW HEADPHN AMP - Bulk |
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