
Detailed Specifications
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Thermal Characteristics
Introduction
The temperature variable in Microsemi’s Designer software refers to the junction temperature, not the
ambient temperature. This is an important distinction because dynamic and static power consumption
cause the chip junction temperature to be higher than the ambient temperature.
EQ 1 can be used to
calculate junction temperature.
TJ = Junction Temperature = ΔT + Ta
EQ 1
Where:
ΔT = θja * P
EQ 2
Where:
Package Thermal Characteristics
The device junction-to-case thermal characteristic is
θjc, and the junction-to-ambient air characteristic is
θja. The thermal characteristics for θja are shown with two different air flow rates. θjc values are provided
for reference. The absolute maximum junction temperature is 125
°C.
The maximum power dissipation allowed for commercial- and industrial-grade devices is a function of
θja.
A sample calculation of the absolute maximum power dissipation allowed for an 896-pin FBGA package
at commercial temperature and still air is as follows:
Ta = Ambient Temperature
ΔT= Temperature gradient between junction (silicon) and ambient
P
=Power
Maximum Power Allowed
°C) Max. ambient temp. (°C)
–
θ
ja(°C/W)
--------------------------------------------------------------------------------------------------------------------------------------------------
125
°C70°C
–
13.6
°C/W
---------------------------------------
4.04 W
=