MPC8347E datasheet(95/108 Pages) FREESCALE

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MPC8347EA PowerQUICC II Pro Integrated Host Processor Hardware Specifications, Rev. 3

Freescale Semiconductor

Thermal

20.2.4

Heat Sinks and Junction-to-Case Thermal Resistance

Some application environments require a heat sink to provide the necessary thermal management of the

device. When a heat sink is used, the thermal resistance is 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 controls the thermal environment to

change the case to ambient thermal resistance, RθCA. For instance, the user can change the size of the heat

sink, the air flow around the device, the interface material, the mounting arrangement on printed circuit

board, or change the thermal dissipation on the printed circuit board surrounding the device.

The thermal performance of devices with heat sinks has been simulated with a few commercially available

heat sinks. The heat sink choice is determined by the application environment (temperature, air flow,

adjacent component power dissipation) and the physical space available. Because there is not a standard

application environment, a standard heat sink is not required.

Table 66 and Table 67 show heat sink thermal resistance for TBGA and PBGA of the MPC8347EA.

Table 66. Heat Sink and Thermal Resistance of MPC8347EA (TBGA)

Heat Sink Assuming Thermal Grease

Air Flow

× 35 mm TBGA

Thermal Resistance

AAVID 30

× 30 × 9.4 mm Pin Fin

Natural Convection

AAVID 30

× 30 × 9.4 mm Pin Fin

1 m/s

6.5

AAVID 30

× 30 × 9.4 mm Pin Fin

2 m/s

5.6

AAVID 31

× 35 × 23 mm Pin Fin

Natural Convection

8.4

AAVID 31

× 35 × 23 mm Pin Fin

1 m/s

4.7

AAVID 31

× 35 × 23 mm Pin Fin

2 m/s

Wakefield, 53

× 53 × 25 mm Pin Fin

Natural Convection

5.7

Wakefield, 53

× 53 × 25 mm Pin Fin

1 m/s

3.5

Wakefield, 53

× 53 × 25 mm Pin Fin

2 m/s

2.7

MEI, 75

× 85 × 12 no adjacent board, extrusion

Natural Convection

6.7

MEI, 75

× 85 × 12 no adjacent board, extrusion

1 m/s

4.1

MEI, 75

× 85 × 12 no adjacent board, extrusion

2 m/s

2.8

MEI, 75

× 85 × 12 mm, adjacent board, 40 mm Side bypass

1 m/s

3.1

MPC8347E Datasheet(PDF) 95 Page - Freescale Semiconductor, Inc

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