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参数资料
| 型号： | 18448 |
| 英文描述： | Microprocessor Family CPU Thermal Management Application Note? 126KB (PDF) |
| 中文描述： | 微处理器系列CPU散热管理应用笔记？ 126KB（PDF格式） |
| 文件页数： | 4/10页 |
| 文件大小： | 126K |
| 代理商： | 18448 |
AMD
CPU Thermal Management
3
APPENDIX
Background Information
Thermal Resistance
Thermal characteristics of integrated circuits (IC) have
long been a major concern for both electronic product
manufacturers and designers. This is because an in-
crease in junction temperature can have an adverse
effect on the long term performance and operating life
of an IC. With the 486 CPU, for example, squeezing 1.2
million transistors on board and running at faster
speeds, more heat is generated which can not be easily
vented out of the computer with the usual fans. Unvent-
ed, the heat builds up and destroys the transistors. Heat
sinks are finding their way into 486 systems but they
may not be good enough for future generations of
CPUs.
The maximum case temperature of some Am486 CPUs
is specified to be 65
°C. The cooling module must dissi-
pate the heat into the ambient air, which must be below
65
°C. How much lower the ambient temperature must
be is given by the thermal resistance times the power.
Therefore, to calculate the maximum ambient temper-
ature that the processor with cooling module can oper-
ate, the following formula is used:
The maximum power consumption (PMax) of the
Am486 processor is given as:
With unit 1 using the thermal grease, the maximum am-
bient temperature for safe operation will be:
For comparison, by using the Thermalloy 2321B-TCM,
the maximum ambient temperature is:
When a transistor is turned on, power is dissipated
equal to the product of the voltage across the collector
junction and the current through it. As a result, the col-
lector junction’s temperature begins to rise. Eventually,
a steady state is reached when the transistor dissipates
the same energy supplied to it. This energy is in the form
of heat and is given off through the case to the surround-
ing environment. The temperature depends upon the
power level and the thermal resistance of the device
package. Thermal resistance is the ability of the pack-
age to conduct heat away from the CPU and into the
surrounding environment. A low thermal resistance val-
ue means that for a given amount of power, the inte-
grated
circuit
junction
will
operate
at
a
lower
temperature, thereby providing a longer life time.
Several variables affect junction temperature. Some are
controlled by the IC vendor, while others are controlled
by the user and the environment in which the device is
used. With the trend toward higher density circuits, in-
creasing circuit complexity and increasing number of
pin outs, total power dissipation is increasing. Hence,
management of thermal characteristics remains a valid
concern.
Thermal resistance (theta jc (
θjc)) is expressed as the
rise in the collector junction temperature (Tj) above the
case temperature (Tc) per unit of power dissipated (Pd)
in the device.
Where
θjc is expressed in °C/W.
Thermal resistance can also be calculated between
junction temperature and ambient temperature (Ta).
Figure 4 illustrates the path of heat flow through a device
with and without a heat sink, and Figure 5 shows a sche-
matic representation of the thermal resistance paths be-
tween the junction and ambient temperatures.
The temperature of the junction (Tj) is related to the
power dissipation and the ambient temperature (Ta) by
the following equation:
If a heat sink is applied, the heat passes from the case
to the sink before being emitted into the air. The purpose
of a heat sink is to increase the effective heat-dissipation
area and quickly remove heat from the device, permit-
ting the device to work at higher power levels. The heat
sink provides an additional low-thermal resistance path
from case to ambient air.
Once a certain case temperature is reached, the maxi-
mum power rating drops off linearly as shown in Figure
6. This is called the derating curve. The derating factor
(Df) is a measure of how fast the curve drops off (i.e.,
the slope of the curve). Its units are in W/
°C. Derating
factor (Df) is the reciprocal of
θjc.
T
Max
Ambient
–
65
P
Max
θ
CA
()
–
=
P
Max
5.35 V
[] 1200 mA
[]
6.3 Watts
=
T
Max
Ambient
–
65
6.3
3.3
() 44.21°C
=
–
=
T
Max
Ambient
–
65
6.3
1.4
() 56.18°C
=
–
=
1
()
θjc
Tj
Tc
–
() Pd
()
=
1a
()
θja
Tj
Ta
–
() Pd
()
=
Tj
Pd
θja
() Ta
+
=
相关PDF资料 |
PDF描述 |
|---|---|
| 1845E | Optoelectronic |
| 1845G | Optoelectronic |
| 1845H | Optoelectronic |
| 1847E | Optoelectronic |
| 1847G | Optoelectronic |
相关代理商/技术参数 |
参数描述 |
|---|---|
| 1844800000 | 制造商:Weidmuller 功能描述:CONN TERM BLOCKS 27 POS 5.08MM SLDR ST TH 10A - Bulk 制造商:Weidmuller 功能描述:LP3R 5.08/27/90 3.2SN OR |
| 1844808 | 功能描述:20 位 端接块 接头，公引脚，带罩（4 面） 0.100"（2.54mm） 90°，直角 通孔 制造商:phoenix contact 系列:COMBICON DMC 包装:带卷（TR） 零件状态:新产品 类型:接头，公引脚，带罩（4 面） 针脚数:20 每级针脚数:10 级别数:2 间距:0.100"（2.54mm） 针座方向:90°，直角 插线入口:- 端子类型:焊接 安装类型:通孔 电流 - IEC:6A 电压 - IEC:160V 电流 - UL:6A 电压 - UL:150V 线规或范围 - AWG:- 线规或范围 -?mm2:- 颜色:黑 工作温度:- 触头配接表面处理:金 特性:固定焊尾 标准包装:300 |
| 1844810000 | 制造商:Weidmuller 功能描述:CONN TERM BLOCKS 33 POS 5.08MM SLDR ST TH 10A - Bulk 制造商:Weidmuller 功能描述:LP3R 5.08/33/90 3.2SN OR |
| 1844811 | 功能描述:22 位 端接块 接头，公引脚，带罩（4 面） 0.100"（2.54mm） 90°，直角 通孔 制造商:phoenix contact 系列:COMBICON DMC 包装:带卷（TR） 零件状态:新产品 类型:接头，公引脚，带罩（4 面） 针脚数:22 每级针脚数:11 级别数:2 间距:0.100"（2.54mm） 针座方向:90°，直角 插线入口:- 端子类型:焊接 安装类型:通孔 电流 - IEC:6A 电压 - IEC:160V 电流 - UL:6A 电压 - UL:150V 线规或范围 - AWG:- 线规或范围 -?mm2:- 颜色:黑 工作温度:- 触头配接表面处理:金 特性:固定焊尾 标准包装:300 |
| 1844820000 | 制造商:Weidmuller 功能描述:CONN TERM BLOCKS 36 POS 5.08MM SLDR ST TH 10A - Bulk 制造商:Weidmuller 功能描述:LP3R 5.08/36/90 3.2SN OR |
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