MPC8349EVVALDB datasheet(75/87 Pages) FREESCALE

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MPC8349EA PowerQUICC II Pro Integrated Host Processor Hardware Specifications, Rev. 13

Freescale Semiconductor

Thermal

20.2

Thermal Management Information

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

See Table 5 for I/O power dissipation values.

20.2.1

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.

20.2.2

Estimation of Junction Temperature with Junction-to-Board

Thermal Resistance

The thermal performance of a device cannot be adequately predicted from the junction-to-ambient thermal

resistance. The thermal performance of any component is strongly dependent on the power dissipation of

surrounding components. In addition, the ambient temperature varies widely within the application. For

many natural convection and especially closed box applications, the board temperature at the perimeter

Junction-to-package natural convection on top

°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 SEMI G38-87 and JEDEC JESD51-2 with the single-layer board horizontal.

3. Per JEDEC JESD51-6 with the board horizontal, 1 m/s is approximately equal to 200 linear feet per minute (LFM).

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 63. Package Thermal Characteristics for TBGA (continued)

Characteristic

Symbol

Value

Unit

Notes

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