MPC866 datasheet(13/96 Pages) NXP

13 / 96 page

MPC866/MPC859 Hardware Specifications, Rev. 2

Freescale Semiconductor

Thermal Calculation and Measurement

Figure 3. Effect of Board Temperature Rise on Thermal Behavior

If the board temperature is known, an estimate of the junction temperature in the environment can be made using

the following equation:

TJ = TB +(RθJB x PD)

where:

RθJB = junction-to-board thermal resistance (ºC/W)

TB = board temperature ºC

PD = power dissipation in package

If the board temperature is known and the heat loss from the package case to the air can be ignored, acceptable

predictions of junction temperature can be made. For this method to work, the board and board mounting must be

similar to the test board used to determine the junction-to-board thermal resistance, namely a 2s2p (board with a

power and a ground plane) and vias attaching the thermal balls to the ground plane.

7.4

Estimation Using Simulation

When the board temperature is not known, a thermal simulation of the application is needed. The simple two-resistor

model can be used with the thermal simulation of the application [2], or a more accurate and complex model of the

package can be used in the thermal simulation.

MPC866 Datasheet(PDF) 13 Page - NXP Semiconductors