MPC8315ECVRAGDA datasheet(103/112 Pages) FREESCALE

103 / 112 page

MPC8315E PowerQUICC™ II Pro Processor Hardware Specifications, Rev. 0

Freescale Semiconductor

103

Thermal (Preliminary)

25.2.3

Experimental Determination of Junction Temperature

To determine the junction temperature of the device in the application after prototypes are available, the

Thermal Characterization Parameter (

ΨJT) can be used to determine the junction temperature with a

measurement of the temperature at the top center of the package case using the following equation:

TJ = TT + (ΨJT × PD)

where:

TJ = junction temperature (°C)

TT = thermocouple temperature on top of package (°C)

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

PD = power dissipation in the package (W)

The thermal characterization parameter is measured per JESD51-2 specification using a 40 gauge type T

thermocouple epoxied to the top center of the package case. The thermocouple should be positioned so

that the thermocouple junction rests on the package. A small amount of epoxy is placed over the

thermocouple junction and over about 1 mm of wire extending from the junction. The thermocouple wire

is placed flat against the package case to avoid measurement errors caused by cooling effects of the

thermocouple wire.

25.2.4

Heat Sinks and Junction-to-Case Thermal Resistance

In some application environments, a heat sink is required 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.

To illustrate the thermal performance of the devices with heat sinks, the thermal performance 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.

MPC8315ECVRAGDA датащи(PDF) 103 Page - Freescale Semiconductor, Inc