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参数资料
| 型号： | MPC8247ZQTMFX |
| 厂商： | FREESCALE SEMICONDUCTOR INC |
| 元件分类： | 微控制器/微处理器 |
| 英文描述： | 32-BIT, 400 MHz, RISC PROCESSOR, PBGA516 |
| 封装： | 27 X 27 MM, 2.25 MM HEIGHT, 1 MM PITCH, PLASTIC, MS-034AAL-1, BGA-516 |
| 文件页数： | 4/60页 |
| 文件大小： | 918K |
| 代理商： | MPC8247ZQTMFX |
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MPC8272 PowerQUICC II Family Hardware Specifications, Rev. 1.5
12
Freescale Semiconductor
Thermal Characteristics
4.2
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 influenced 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 air flow 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 flows through the case and the heat sink
to the ambient environment. For most packages, a better model is required.
4.3
Estimation with Junction-to-Board Thermal Resistance
A simple package thermal model which 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 thermal resistance 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, especially PBGA packages, is
strongly dependent on the board temperature.
If the board temperature is known, an estimate of the junction temperature in the environment can be made
using the following equation:
TJ = TB + (RθJB × PD)
where:
RθJB = junction-to-board thermal resistance (C/W)
TB = board temperature (C)
PD = power dissipation in package
If the board temperature is known and the heat loss from the package case to the air can be ignored,
acceptable predictions of junction temperature can be made. For this method to work, the board and board
mounting must be similar to the test board used to determine the junction-to-board thermal resistance,
namely a 2s2p (board with a power and a ground plane) and by attaching the thermal balls to the ground
plane.
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