AX2000 datasheet(20/262 Pages) MICROSEMI

20 / 262 page

Detailed Specifications

2- 6

R ev isio n 1 8

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

=Power

θja = Junction to ambient of package. θja numbers are located under Table 2-6 on page 2-7.

Maximum Power Allowed

Max. junction temp. (

°C) Max. ambient temp. (°C)

–

ja(°C/W)

--------------------------------------------------------------------------------------------------------------------------------------------------

125

°C70°C

–

13.6

°C/W

---------------------------------------

4.04 W

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