参数资料
型号: MPC870ZT133
厂商: MOTOROLA INC
元件分类: 微控制器/微处理器
英文描述: 32-BIT, 133 MHz, RISC PROCESSOR, PBGA256
封装: 23 X 23 MM, PLASTIC, BGA-256
文件页数: 4/84页
文件大小: 1352K
代理商: MPC870ZT133
12
MPC875/MPC870 Hardware Specifications
MOTOROLA
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
Thermal Calculation and Measurement
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, 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 airflow 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.
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
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 and 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 vias attaching the thermal balls to the ground
plane.
相关PDF资料
PDF描述
MPC875ZT80 32-BIT, 80 MHz, RISC PROCESSOR, PBGA256
MPC880VR80 32-BIT, 80 MHz, RISC PROCESSOR, PBGA357
MPC885CVR133 32-BIT, 133 MHz, RISC PROCESSOR, PBGA357
MPC885ZP66 32-BIT, 66 MHz, RISC PROCESSOR, PBGA357
MPC885CZP133 32-BIT, 133 MHz, RISC PROCESSOR, PBGA357
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