MPC8272 datasheet(14/61 Pages) FREESCALE

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MPC8272 PowerQUICC II Family Hardware Specifications, Rev. 3

Freescale Semiconductor

Thermal Characteristics

This table describes thermal characteristics. See Table 2 for information on a given SoC’s package.

Discussions of each characteristic are provided in Section 4.1, “Estimation with Junction-to-Ambient

Thermal Resistance,” through Section 4.7, “References.” For the these discussions, PD =(VDD × IDD) +

PI/O, where PI/O is the power dissipation of the I/O drivers.

4.1

Estimation with Junction-to-Ambient Thermal Resistance

An estimation of the chip junction temperature, TJ, in C can be obtained from the following equation:

TJ = TA + (RθJA × PD)

where:

TA = ambient temperature (ºC)

RθJA = package junction-to-ambient thermal resistance (ºC/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.

4 MPC8280, MPC8275VR, MPC8275ZQ only.

Table 7. Thermal Characteristics

Characteristic

Symbol

Value

Unit

Air Flow

Junction-to-ambient—

single-layer board1

1 Assumes no thermal vias

RθJA

°C/W

Natural convection

1 m/s

Junction-to-ambient—

four-layer board

RθJA

°C/W

Natural convection

1 m/s

Junction-to-board2

2 Thermal resistance between the die and the printed circuit board per JEDEC JESD51-8. Board temperature is

measured on the top surface of the board near the package.

RθJB

°C/W

—

Junction-to-case3

3 Thermal resistance between the die and the case top surface as measured by the cold plate method (MIL SPEC-883

Method 1012.1).

RθJC

°C/W

—

Junction-to-package top4

4 Thermal characterization parameter indicating the temperature difference between package top and the junction

temperature per JEDEC JESD51-2. When Greek letters are not available, the thermal characterization parameter is

written as Psi-JT.

RθJT

°C/W

—

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