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參數(shù)資料
| 型號： | LM4951 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Wide Voltage Range 1.8 Watt Audio Amplifier |
| 中文描述： | 寬電壓范圍1.8瓦音頻功率放大器 |
| 文件頁數(shù)： | 11/18頁 |
| 文件大?。?/td> | 1119K |
| 代理商： | LM4951 |
Application Information
HIGH VOLTAGE BOOMER
Unlike previous 5V Boomer
amplifiers, the LM4951 is de-
signed to operate over a power supply voltages range of
2.7V to 9V. Operating on a 7.5V power supply, the LM4951
will deliver 1.8W into an 8
BTL load with no more than 1%
THD+N.
BRIDGE CONFIGURATION EXPLANATION
As shown in Figure 1, the LM4951 consists of two opera-
tional amplifiers that drive a speaker connected between
their outputs. The value of input and feedback resistors
determine the gain of each amplifier. External resistors R
i
and R
set the closed-loop gain of AMP
, whereas two 20k
internal resistors set AMP
’s gain to -1. The LM4951 drives
a load, such as a speaker, connected between the two
amplifier outputs, V
+ and V
-. Figure 1 shows that AMP
’s
output serves asAMP
’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 AMP
and AMP
and driven differentially
(commonly referred to as "bridge mode"). This results in a
differential, or BTL, 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. 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. To ensure minimum
output signal clipping when choosing an amplifier’s closed-
loop gain, refer to the
AUDIO POWER AMPLIFIER DESIGN
section. Under rare conditions, with unique combinations of
high power supply voltage and high closed loop gain set-
tings, the LM4951 may exhibit low frequency oscillations.
Another advantage of the differential bridge output is no net
DC voltage across the load. This is accomplished by biasing
AMP1’s and AMP2’s outputs at half-supply. This eliminates
the coupling capacitor that single supply, single-ended am-
plifiers require. Eliminating an output coupling capacitor in a
typical single-ended configuration forces a single-supply am-
plifier’s half-supply bias voltage across the load. This in-
creases internal IC power dissipation and may permanently
damage loads such as speakers.
POWER DISSIPATION
Power dissipation is a major concern when designing a
successful bridged amplifier.
The LM4951’s dissipation when driving a BTL load is given
by Equation (2). For a 7.5V supply and a single 8
BTL load,
the dissipation is 1.42W.
P
DMAX-MONOBTL
= 4(V
DD
)
2
/
2
π
2
R
L
:
Bridge Mode (2)
The maximum power dissipation point given by Equation (2)
must not exceed the power dissipation given by Equation
(3):
P
DMAX
’ = (T
JMAX
- T
A
)
/
θ
JA
(3)
The LM4951’s T
= 150C. In the SD package, the
LM4951’s
θ
is 73C/W when the metal tab is soldered to a
copper plane of at least 1in
2
. This plane can be split between
the top and bottom layers of a two-sided PCB. Connect the
two layers together under the tab with an array of vias.At any
given ambient temperature T
A
, use Equation (3) to find the
maximum internal power dissipation supported by the IC
packaging. Rearranging Equation (3) and substituting P
DMAX
for P
DMAX
’ results in Equation (4). This equation gives the
maximum ambient temperature that still allows maximum
stereo power dissipation without violating the LM4951’s
maximum junction temperature.
T
A
= T
JMAX
- P
DMAX-MONOBTL
θ
JA
(4)
For a typical application with a 7.5V power supply and a BTL
8
load, the maximum ambient temperature that allows
maximum stereo power dissipation without exceeding the
maximum junction temperature is approximately 46C for the
TS package.
T
JMAX
= P
DMAX-MONOBTL
θ
JA
+ T
A
(5)
Equation (5) gives the maximum junction temperature
T
. If the result violates the LM4951’s 150C, reduce the
maximum junction temperature by reducing the power sup-
ply voltage or increasing the load resistance. Further allow-
ance should be made for increased ambient temperatures.
The above examples assume that a device is operating
around the maximum power dissipation point. Since internal
power dissipation is a function of output power, higher am-
bient temperatures are allowed as output power or duty
cycle decreases.
If the result of Equation (2) is greater than that of Equation
(3), then decrease the supply voltage, increase the load
impedance, or reduce the ambient temperature. Further,
ensure that speakers rated at a nominal 8
do not fall below
6
. If these measures are insufficient, a heat sink can be
added to reduce
θ
. The heat sink can be created using
additional copper area around the package, with connec-
tions to the ground pins, supply pin and amplifier output pins.
Refer to the
Typical Performance Characteristics
curves
for power dissipation information at lower output power lev-
els.
POWER SUPPLY VOLTAGE LIMITS
Continuous proper operation is ensured by never exceeding
the voltage applied to any pin, with respect to ground, as
listed in the Absolute Maximum Ratings section.
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is
critical for low noise performance and high power supply
rejection. Applications that employ a voltage regulator typi-
cally use a 10μF in parallel with a 0.1μF filter capacitors to
stabilize the regulator’s output, reduce noise on the supply
line, and improve the supply’s transient response. However,
their presence does not eliminate the need for a local 1.0μF
tantalum bypass capacitance connected between the
LM4951’s supply pins and ground. Do not substitute a ce-
ramic capacitor for the tantalum. Doing so may cause oscil-
L
www.national.com
11
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM4951A | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Wide Voltage Range 1.8 Watt Audio Amplifier With Short Circuit Protection |
| LM4951ASD | 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 |
| LM4951ASD/NOPB | 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 |
| LM4951ASDBD | 功能描述:BOARD EVALUATION FOR LM4951A 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:- |
| LM4951ASDBD/NOPB | 功能描述:音頻 IC 開發(fā)工具 LM4951ASD 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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