MPC8272EC datasheet(12/60 Pages) FREESCALE

12 / 60 page

MPC8272 PowerQUICC II™ Family Hardware Specifications, Rev. 2

Freescale Semiconductor

Thermal Characteristics

Table 6 describes thermal characteristics. Refer to Table 2 for information on a given device’s package.

Discussions of each characteristic are provided in sections 4.1 through 4.7. 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 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 which 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.

4.2

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:

MPC8272 and MPC8271 only.

Table 6. Thermal Characteristics

Characteristic

Symbol

Value

Unit

Air Flow

Junction-to-ambient—

single-layer board 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-board 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-case 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 top 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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