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參數(shù)資料
| 型號(hào)： | MPC866T |
| 廠商： | 飛思卡爾半導(dǎo)體(中國(guó))有限公司 |
| 英文描述： | Hardware Specifications |
| 中文描述： | 硬件規(guī)格 |
| 文件頁(yè)數(shù)： | 4/92頁(yè) |
| 文件大?。?/td> | 1274K |
| 代理商： | MPC866T |
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MPC866/859 Hardware Specications
MOTOROLA
Thermal Calculation and Measurement
7.1
Estimation with Junction-to-Ambient Thermal
Resistance
An estimation of the chip junction temperature, TJ, in °C can be obtained from the equation:
TJ = TA +(RθJA x PD)
where:
TA = ambient temperature (C)
RθJA = package junction-to-ambient thermal resistance (C/W)
PD = power dissipation in package
The junction-to-ambient thermal resistance is an industry standard value that provides a quick and easy
estimation of thermal performance. However, the answer is only an estimate; test cases have demonstrated
that errors of a factor of two (in the quantity TJ-TA) are possible.
7.2
Estimation with Junction-to-Case Thermal Resistance
Historically, the thermal resistance has frequently been expressed as the sum of a junction-to-case thermal
resistance and a case-to-ambient thermal resistance:
RθJA = RθJC + RθCA
where:
RθJA = junction-to-ambient thermal resistance (C/W)
RθJC = junction-to-case thermal resistance (C/W)
RθCA = case-to-ambient thermal resistance (C/W)
RθJC is device related and cannot be inuenced by the user. The user adjusts the thermal environment to
affect the case-to-ambient thermal resistance, RθCA. For instance, the user can change the airow around
the device, add a heat sink, change the mounting arrangement on the printed-circuit board, or change the
thermal dissipation on the printed-circuit board surrounding the device. This thermal model is most useful
for ceramic packages with heat sinks where some 90% of the heat ows through the case and the heat sink
to the ambient environment. For most packages, a better model is required.
7.3
Estimation with Junction-to-Board Thermal Resistance
A simple package thermal model that has demonstrated reasonable accuracy (about 20%) is a two-resistor
model consisting of a junction-to-board and a junction-to-case thermal resistance. The junction-to-case
covers the situation where a heat sink is used or where a substantial amount of heat is dissipated from the
top of the package. The junction-to-board thermal resistance describes the thermal performance when most
of the heat is conducted to the printed-circuit board. It has been observed that the thermal performance of
most plastic packages and especially PBGA packages is strongly dependent on the board temperature; see
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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