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參數(shù)資料
| 型號(hào)： | LM4804 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Low Voltage High Power Audio Power Amplifier |
| 中文描述： | 高功率低電壓音頻功率放大器 |
| 文件頁(yè)數(shù)： | 8/16頁(yè) |
| 文件大?。?/td> | 820K |
| 代理商： | LM4804 |
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Application Information
BRIDGE CONFIGURATION EXPLANATION
Audio Amplifier portion of the LM4804 has two operational
amplifiers internally, allowing for a few different amplifier
configurations. 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 Rf to Ri while
the second amplifier’s gain is fixed by the two internal 20k
resistors. Figure 1 shows that the output of amplifier one
serves as the input to amplifier two which results in both
amplifiers producing signals identical in magnitude, but out
of phase by 180. Consequently, the differential gain for the
IC is
A
VD
= 2 *(Rf/Ri)
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 the 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 con-
ditions. 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.
Abridge configuration also creates a second advantage over
single-ended amplifiers. 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 configuration. Without an output cou-
pling capacitor, the half-supply bias across the load would
result in both increased internal IC power dissipation and
also possible loudspeaker damage.
AMPLIFIER POWER DISSIPATION
Power dissipation is a major concern when designing a
successful amplifier, whether the amplifier is bridged or
single-ended. A direct consequence of the increased power
delivered to the load by a bridge amplifier is an increase in
internal power dissipation. Since the amplifier portion of the
LM4804 has two operational amplifiers, the maximum inter-
nal power dissipation is 4 times that of a single-ended am-
plifier. The maximum power dissipation for a given BTL
application can be derived from Equation 1.
P
DMAX(AMP)
= 4(V
DD
)
2
/ (2
π
2
R
L
)
(1)
BOOST CONVERTER POWER DISSIPATION
At higher duty cycles, the increased ON time of the FET
means the maximum output current will be determined by
power dissipation within the LM2731 FET switch. The switch
power dissipation from ON-state conduction is calculated by
Equation 2.
P
DMAX(SWITCH)
= DC x I
IND
(AVE)
2
x R
DS
(ON)
(2)
There will be some switching losses as well, so some derat-
ing needs to be applied when calculating IC power dissipa-
tion.
TOTAL POWER DISSIPATION
The total power dissipation for the LM4804 can be calculated
by adding Equation 1 and Equation 2 together to establish
Equation 3:
P
DMAX(TOTAL)
= [4*(V
DD
)
2
/
2
π
2
R
L
]+[DCxI
IND
(AVE)
2
xR
DS
(ON)]
(3)
The result from Equation 3 must not be greater than the
power dissipation that results from Equation 4:
P
DMAX
= (T
JMAX
- T
A
) /
θ
JA
(4)
For package LQA28A,
θ
= 59C/W. T
= 125C for the
LM4804. Depending on the ambient temperature, T
, of the
system surroundings, Equation 4 can be used to find the
maximum internal power dissipation supported by the IC
packaging. If the result of Equation 3 is greater than that of
Equation 4, then either the supply voltage must be in-
creased, the load impedance increased or T
reduced. For
the typical application of a 3V power supply, with V1 set to
6.0V and 8
load, the maximum ambient temperature pos-
sible without violating the maximum junction temperature is
approximately TBDC provided that device operation is
around the maximum power dissipation point. Thus, for typi-
cal applications, power dissipation is not an issue. Power
dissipation is a function of output power and thus, if typical
operation is not around the maximum power dissipation
point, the ambient temperature may be increased accord-
ingly. Refer to the Typical Performance Characteristics
curves for power dissipation information for lower output
levels.
EXPOSED-DAP PACKAGE PCB MOUNTING
CONSIDERATIONS
The LM4804’s exposed-DAP (die attach paddle) package
(LD) 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 surrounding air. The
LD package should have its DAP soldered to a copper pad
on the PCB. The DAP’s PCB copper pad may be connected
to a large plane of continuous unbroken copper. This plane
forms a thermal mass, heat sink, and radiation area. Further
detailed and specific information concerning PCB layout,
fabrication, and mounting an LD (LLP) package is available
from National Semiconductor’s Package Engineering Group
under application note AN1187.
SHUTDOWN FUNCTION
In many applications, a microcontroller or microprocessor
output is used to control the shutdown circuitry to provide a
quick, smooth transition into shutdown.Another solution is to
use a single-pole, single-throw switch, in conjunction with an
external pull-up resistor to drive both shutdown pins simul-
taneously. When the switch is closed, the shutdown pin is
connected to ground which disables the amplifier. If the
switch is open, then the external pull-up resistor to V
DD
will
enable the LM4804. This scheme guarantees that the shut-
down pins will not float thus preventing unwanted state
changes.
L
www.national.com
8
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| LM4804LQ | Low Voltage High Power Audio Power Amplifier |
| LM4817 | Circular Connector; MIL SPEC:MIL-C-5015; Body Material:Metal; Series:GT; No. of Contacts:85; Connector Shell Size:40; Connecting Termination:Crimp; Circular Shell Style:Wall Mount Receptacle; Body Style:Straight |
| LM4849 | Stereo 2W Audio Power Amplifiers with DC Volume Control and Input Mux |
| LM4849MH | Stereo 2W Audio Power Amplifiers with DC Volume Control and Input Mux |
| LM4852 | Integrated Audio Amplifier System |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM4804LQ | 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 |
| LM4804LQ/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 |
| LM4804LQX | 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 |
| LM4804LQX/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 |
| LM4805 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:3V, 1W Boosted Boomer |
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