MPC5645S datasheet(67/146 Pages) FREESCALE

67 / 146 page

Qorivva MPC5645S Microcontroller Data Sheet, Rev. 8

Freescale Semiconductor

A more accurate two-resistor thermal model can be constructed from the junction-to-board thermal resistance and the

junction-to-case thermal resistance. The junction-to-case thermal resistance describes when using a heat sink or where a

substantial amount of heat is dissipated from the top of the package. The junction-to-board thermal resistance describes the

thermal performance when most of the heat is conducted to the printed circuit board. This model can be used to generate simple

estimations and for computational fluid dynamics (CFD) thermal models.

To determine the junction temperature of the device in the application on a prototype board, use the thermal characterization

parameter (



JT) to determine the junction temperature by measuring the temperature at the top center of the package case using

the following equation:

TJ = TT + (JT x PD)

Eqn. 4

where:

TT= thermocouple temperature on top of the package (

oC)



JT= thermal characterization parameter (

oC/W)

PD= power dissipation in the package (W)

The thermal characterization parameter is measured in compliance with the JESD51-2 specification using a 40-gauge type T

thermocouple epoxied to the top center of the package case. Position the thermocouple so that the thermocouple junction rests

on the package. Place a small amount of epoxy on the thermocouple junction and approximately 1 mm of wire extending from

the junction. Place the thermocouple wire flat against the package case to avoid measurement errors caused by the cooling

effects of the thermocouple wire.

References:

Semiconductor Equipment and Materials International

805 East Middlefield Rd.

Mountain View, CA 94043

(415) 964-5111

MIL-SPEC and EIA/JESD (JEDEC) specifications are available from Global Engineering Documents at 800-854-7179 or

303-397-7956.

JEDEC specifications are available on the WEB at http://www.jedec.org.

MPC5645S Datasheet(PDF) 67 Page - Freescale Semiconductor, Inc