2.1.4.2 Theta-JA

Junction-to-ambient thermal resistance (θJA) is determined under standard conditions specified by JEDEC (JESD-51), but it has little relevance in actual performance of the product. It should be used with caution but is useful for comparing the thermal performance of one package to another.

A sample calculation showing the maximum power dissipation allowed for the A2F500-FG484 package under forced convection of 1.0 m/s and 75 °C ambient temperature is as follows:

Figure 2-6. EQ 4
where:
  • θJA = 18.6 °C/W (taken from Table 2-6.)
  • TA = 75.00 °C
Figure 2-7. EQ 5

The power consumption of a device can be calculated using the Microchip SoC Products Group power calculator. The device's power consumption must be lower than the calculated maximum power dissipation by the package. If the power consumption is higher than the device's maximum allowable power dissipation, a heat sink can be attached on top of the case, or the airflow inside the system must be increased.