MPC8378E datasheet(116/128 Pages) FREESCALE

116 / 128 page

MPC8378E PowerQUICC II Pro Processor Hardware Specifications, Rev. 8

116

Freescale Semiconductor

23.2

Thermal Management Information

For the following sections, PD = (VDD × IDD) + PI/O where PI/O is the power dissipation of the I/O drivers.

23.2.1

Estimation of Junction Temperature with Junction-to-Ambient

Thermal Resistance

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

TJ = TA + (RθJA × PD)

where:

TJ = junction temperature (°C)

TA = ambient temperature for the package (°C)

RθJA = junction to ambient thermal resistance (°C/W)

PD = power dissipation in the package (W)

The junction to ambient thermal resistance is an industry-standard value that provides a quick and easy

estimation of thermal performance. Generally, the value obtained on a single layer board is appropriate for

a tightly packed printed circuit board. The value obtained on the board with the internal planes is usually

appropriate if the board has low power dissipation and the components are well separated. Test cases have

demonstrated that errors of a factor of two (in the quantity TJ – TA) are possible.

23.2.2

Estimation of Junction Temperature with Junction-to-Board

Thermal Resistance

NOTE

The heat sink cannot be mounted on the package.

Junction-to-package natural convection on top

ψJT

°C/W

Notes:

1. Junction temperature is a function of die size, on-chip power dissipation, package thermal resistance, mounting site (board)

temperature, ambient temperature, air flow, power dissipation of other components on the board, and board thermal

resistance.

2. Per JEDEC JESD51-2 with the single layer board horizontal. Board meets JESD51-9 specification.

3. Per JEDEC JESD51-6 with the board horizontal.

4. 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.

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

1012.1).

6. 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.

Table 77. Package Thermal Characteristics for TePBGA II (continued)

Parameter

Symbol

Value

Unit

Note

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