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参数资料
| 型号： | LM3875MDC |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 音频／视频放大 |
| 英文描述： | 56 W, 1 CHANNEL, AUDIO AMPLIFIER, UUC |
| 封装： | DIE |
| 文件页数： | 3/21页 |
| 文件大小： | 582K |
| 代理商： | LM3875MDC |
Application Information (Continued)
heat sink design and the mounting of the IC to the heat sink.
For the design of a heat sink for your audio amplifier applica-
tion refer to the Determining the Correct Heat Sink sec-
tion.
Since a semiconductor manufacturer has no control over
which heat sink is used in a particular amplifier design, we
can only inform the system designer of the parameters and
the method needed in the determination of a heat sink. With
this in mind, the system designer must choose his supply
voltages, a rated load, a desired output power level, and
know the ambient temperature surrounding the device.
These parameters are in addition to knowing the maximum
junction temperature and the thermal resistance of the IC,
both of which are provided by National Semiconductor.
As a benefit to the system designer we have provided Maxi-
mum Power Dissipation vs Supply Voltages curves for vari-
ous loads in the Typical Performance Characteristics sec-
tion, giving an accurate figure for the maximum thermal
resistance required for a particular amplifier design. This
data was based on
θ
JC = 1C/W and θCS = 0.2C/W. We also
provide a section regarding heat sink determination for any
audio amplifier design where
θ
CS may be a different value. It
should be noted that the idea behind dissipating the maxi-
mum power within the IC is to provide the device with a low
resistance to convection heat transfer such as a heat sink.
Therefore, it is necessary for the system designer to be con-
servative in his heat sink calculations. As a rule, the lower
the thermal resistance of the heat sink the higher the amount
of power that may be dissipated. This is, of course, guided
by the cost and size requirements of the system. Convection
cooling heat sinks are available commercially, and their
manufacturers should be consulted for ratings.
Proper mounting of the IC is required to minimize the thermal
drop between the package and the heat sink. The heat sink
must also have enough metal under the package to conduct
heat from the center of the package bottom to the fins with-
out excessive temperature drop.
A thermal grease such as Wakefield type 120 or Thermalloy
Thermacote should be used when mounting the package to
the heat sink. Without this compound, the thermal resistance
will be no better than 0.5C/W, and probably much worse.
With the compound, thermal resistance will be 0.2C/W or
less, assuming under 0.005 inch combined flatness runout
for the package and heat sink. Proper torquing of the mount-
ing bolts is important and can be determined from heat sink
manufacturer’s specification sheets.
Should it be necessary to isolate V from the heat sink, an in-
sulating washer is required. Hard washers like berylum ox-
ide, anodized aluminum and mica require the use of thermal
compound on both faces. Two-mil mica washers are most
common, giving about 0.4C/W interface resistance with the
compound.
Silicone-rubber washers are also available. A 0.5C/W ther-
mal resistance is claimed without thermal compound. Expe-
rience has shown that these rubber washers deteriorate and
must be replaced should the IC be dismounted.
Determining Maximum Power Dissipation
Power dissipation within the integrated circuit package is a
very important parameter requiring a thorough understand-
ing if optimum power output is to be obtained. An incorrect
maximum power dissipation (P
D) calculation may result in in-
adequate heatsinking, causing thermal shutdown circuitry to
operate and limit the output power.
The following equations can be used to accurately calculate
the maximum and average integrated circuit power dissipa-
tion for your amplifier design, given the supply voltage, rated
load, and output power. These equations can be directly ap-
plied to the Power Dissipation vs Output Power curves in the
Typical Performance Characteristics section.
Equation (1) exemplifies the maximum power dissipation of
the IC and
Equations (2), (3) exemplify the average IC power
dissipation expressed in different forms.
P
DMAX =VCC
2/2
π2 R
L
(1)
where V
CC is the total supply voltage
P
DAVE =(VOpk/RL)[VCC/π VOpk/2]
(2)
where V
CC is the total supply voltage and VOpk =VCC/π
P
DAVE =VCC VOpk/π RL VOpk
2/2 R
L
(3)
where V
CC is the total supply voltage.
Determining the Correct Heat Sink
Once the maximum IC power dissipation is known for a
given supply voltage, rated load, and the desired rated out-
put power the maximum thermal resistance (in C/W) of a
heat sink can be calculated. This calculation is made using
Equation (4) and is based on the fact that thermal heat flow
parameters are analogous to electrical current flow proper-
ties.
It is also known that typically the thermal resistance,
θ
JC
(junction to case), of the LM3875 is 1C/W and that using
Thermalloy Thermacote thermal compound provides a ther-
mal resistance,
θ
CS (case to heat sink), of about 0.2C/W as
explained in the Heat Sinking section.
Referring to the figure below, it is seen that the thermal resis-
tance from the die (junction) to the outside air (ambient) is a
combination of three thermal resistances, two of which are
known,
θ
JC and θCS. Since convection heat flow (power dis-
sipation) is analogous to current flow, thermal resistance is
analogous to electrical resistance, and temperature drops
are analogous to voltage drops, the power dissipation out of
the LM3875 is equal to the following:
P
DMAX =(TJmax TAmb)/θJA
where
θ
JA = θJC + θCS + θSA
But since we know P
DMAX, θJC, and θSC for the application
and we are looking for
θ
SA, we have the following:
θ
SA = [(TJmax TAmb)PDMAX (θJC + θCS)]/PDMAX
(4)
Again it must be noted that the value of
θ
SA is dependent
upon the system designer’s amplifier application and its cor-
responding parameters as described previously. If the ambi-
ent temperature that the audio amplifier is to be working un-
der is higher than the normal 25C, then the thermal
resistance for the heat sink, given all other things are equal,
will need to be smaller.
Equations (1), (4) are the only equations needed in the de-
termination of the maximum heat sink thermal resistance.
This is, of course, given that the system designer knows the
required supply voltages to drive his rated load at a particular
power output level and the parameters provided by the semi-
conductor manufacturer. These parameters are the junction
DS011449-10
LM3875
www.national.com
11
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相关代理商/技术参数 |
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|---|---|
| LM3875T | 功能描述:IC AMP AUDIO PWR 56W AB TO220-11 RoHS:是 类别:集成电路 (IC) >> 线性 - 音頻放大器 系列:Overture™ 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:DirectDrive® 类型:H 类 输出类型:耳机，2-通道（立体声） 在某负载时最大输出功率 x 通道数量:35mW x 2 @ 16 欧姆 电源电压:1.62 V ~ 1.98 V 特点:I²C，麦克风，静音，短路保护，音量控制 安装类型:表面贴装 供应商设备封装:25-WLP（2.09x2.09） 封装/外壳:25-WFBGA，WLCSP 包装:带卷 (TR) |
| LM3875T | 制造商:Texas Instruments 功能描述:IC AMP AUDIO 100W 3875 SIL-11 |
| LM3875T/NOPB | 制造商:Texas Instruments 功能描述:Audio Amp Speaker 1-CH Mono 56W Class-AB 11-Pin(11+Tab) TO-220 |
| LM3875TF | 功能描述:音频放大器 RoHS:否 制造商:STMicroelectronics 产品:General Purpose Audio Amplifiers 输出类型:Digital 输出功率: THD + 噪声: 工作电源电压:3.3 V 电源电流: 最大功率耗散: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:TQFP-64 封装:Reel |
| LM3875TF/NOPB | 功能描述:音频放大器 RoHS:否 制造商:STMicroelectronics 产品:General Purpose Audio Amplifiers 输出类型:Digital 输出功率: THD + 噪声: 工作电源电压:3.3 V 电源电流: 最大功率耗散: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:TQFP-64 封装:Reel |
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