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參數(shù)資料
| 型號(hào)： | LM4876 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | 1.1W Audio Power Amplifier with Shutdown Logic Low |
| 中文描述： | 1.1W音頻功率放大器，帶有關(guān)斷邏輯低 |
| 文件頁數(shù)： | 6/9頁 |
| 文件大?。?/td> | 247K |
| 代理商： | LM4876 |
Application Information
Demo Board Schematic
BRIDGE CONFIGURATION EXPLANATION
As shown in Figure 1 the LM4876 has two operational am-
plifiers internally, allowing for a few different amplifier con-
figurations. The first amplifier’s gain is externally config-
urable, while the second amplifier is internally fixed in a
unity-gain, inverting configuration. The closed-loop gain of
the first amplifier is set by selecting the ratio of R
to R
while
the second amplifier’s gain is fixed by the two internal 40 k
resistors. Figure 1 shows that the output of amplifier one
serves as the input to amplifier two which results in both am-
plifiers producing signals identical in magnitude, but out of
phase 180. Consequently, the differential gain for the IC is
A
VD
= 2 *(R
f
/R
i
)
By driving the load differentially through outputs Vo1 and
Vo2, an amplifier configuration commonly referred to as
“bridged mode” is established. Bridged mode operation is
different from the classical single-ended amplifier configura-
tion where one side of its load is connected to ground.
A bridge amplifier design has a few distinct advantages over
the single-ended configuration, as it provides differential
drive to the load, thus doubling output swing for a specified
supply voltage. Four times the output power is possible as
compared to a single-ended amplifier under the same condi-
tions. This increase in attainable output power assumes that
the amplifier is not current limited or clipped. In order to
choose an amplifier’s closed-loop gain without causing ex-
cessive clipping, please refer to the
Audio Power Amplifier
Design
section.
A bridge configuration, such as the one used in LM4876,
also creates a second advantage over single-ended amplifi-
ers. Since the differential outputs, Vo1 and Vo2, are biased
at half-supply, no net DC voltage exists across the load. This
eliminates the need for an output coupling capacitor which is
required in a single supply, single-ended amplifier configura-
tion. Without an output coupling capacitor, the half-supply
bias across the load would result in both increased internal
IC power dissipation and also possible loudspeaker damage.
POWER DISSIPATION
Power dissipation is a major concern when designing a suc-
cessful amplifier, whether the amplifier is bridged or single-
ended. A direct consequence of the increased power deliv-
ered to the load by a bridge amplifier is an increase in
internal power dissipation. Equation 1 states the maximum
power dissipation point for a bridge amplifier operating at a
given supply voltage and driving a specified output load.
P
DMAX
= 4*(V
DD
)
2
/(2
π
2
R
L
)
Since the LM4876 has two operational amplifiers in one
package, the maximum internal power dissipation is 4 times
that of a single-ended ampifier. Even with this substantial in-
crease in power dissipation, the LM4876 does not require
heatsinking under most operating conditions and output
loading. From Equation 1, assuming a 5V power supply and
an 8
load, the maximum power dissipation point is
625 mW. The maximum power dissipation point obtained
from Equation 1 must not be greater than the power dissipa-
tion that results from Equation 2:
P
DMAX
= (T
JMAX
–T
A
)/
θ
JA
For package M08A,
θ
= 140C/W, assuming free air opera-
tion. T
= 150C for the LM4876. The
θ
can be de-
creased by using some form of heat sinking. The resultant
θ
will be the summation of the
θ
JC
,
θ
, and
θ
.
θ
is the
junction to case of the package,
θ
is the case to heat sink
thermal resistance and
θ
is the heat sink to ambient ther-
mal resistance. By adding additional copper area around the
LM4876, the
θ
JA
can be reduced from its free air value of
140C/W for package M08A. Depending on the ambient tem-
perature, T
A
, and the
θ
JA
, Equation 2 can be used to find the
maximum internal power dissipation supported by the IC
packaging. If the result of Equation 1 is greater than that of
Equation 2, then either the supply voltage must be de-
creased, the load impedance increased, the
θ
decreased,
or the ambient temperature reduced. For the typical applica-
tion of a 5V power supply, with an 8
load, and no additional
heatsinking, the maximum ambient temperature possible
without violating the maximum junction temperature is ap-
proximately 61C provided that device operation is around
the maximum power dissipation point and assuming surface
mount packaging. Internal power dissipation is a function of
output power. If typical operation is not around the maximum
power dissipation point, the ambient temperature can be in-
creased. Refer to the
Typical Performance Characteris-
tics
curves for power dissipation information for different out-
put powers and output loading.
(1)
(2)
POWER SUPPLY BYPASSING
As with any amplifier, proper supply bypassing is critical for
low noise performance and high power supply rejection. The
capacitor location on both the bypass and power supply pins
should be as close to the device as possible. Typical applica-
tions employ a 5V regulator with 10 μF and a 0.1 μF bypass
capacitors which aid in supply stability. This does not elimi-
nate the need for bypassing the supply nodes of the
LM4876. The selection of bypass capacitors, especially C
B
,
is dependent upon PSRR requirements, click and pop per-
formance as explained in the section,
Proper Selection of
External Components
, system cost, and size constraints.
SHUTDOWN FUNCTION
In order to reduce power consumption while not in use, the
LM4876 contains a shutdown pin to externally turn off the
amplifier’s bias circuitry. This shutdown feature turns the am-
plifier off when a logic low is placed on the shutdown pin. By
switching the shutdown pin to ground, the LM4876 supply
DS101299-24
L
www.national.com
6
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM4876_03 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:1.1W Audio Power Amplifier with Logic Low Shutdown |
| LM4876M | 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 |
| LM4876M/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 |
| LM4876MM | 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 |
| LM4876MM/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 |
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