Axcelerator Family FPGAs
2- 6
v2.8
Thermal Characteristics
Introduction
The temperature variable in Actel’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 2-1 can be used to calculate junction temperature.
TJ = Junction Temperature = ΔT + Ta
EQ 2-1
Where:
ΔT = θ
ja * P
EQ 2-2
Where:
Package Thermal Characteristics
The device junction-to-case thermal characteristic is
θ
jc, and the junction-to-ambient air characteristic is θja. The
thermal characteristics for
θ
ja 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:
The maximum power dissipation allowed for Military temperature and Mil-Std 883B devices is specified as a function
of
θ
jc.
Ta = Ambient Temperature
ΔT = Temperature gradient between junction
(silicon) and ambient
P= Power
θ
ja
= Junction to ambient of package.
θ
ja numbers
Table 2-6 Package Thermal Characteristics
Package Type
Pin Count
θ
jc
θ
ja Still Air
θ
ja 1.0m/s
θ
ja 2.5m/s
Units
Chip Scale Package (CSP)
180
N/A
57.8
51.0
50
°C/W
Plastic Quad Flat Pack (PQFP)
208
8.0
26
23.5
20.9
°C/W
Plastic Ball Grid Array (PBGA)
729
2.2
13.7
10.6
9.6
°C/W
Fine Pitch Ball Grid Array (FBGA)
256
3.0
26.6
22.8
21.5
°C/W
Fine Pitch Ball Grid Array (FBGA)
324
3.0
25.8
22.1
20.9
°C/W
Fine Pitch Ball Grid Array (FBGA)
484
3.2
20.5
17.0
15.9
°C/W
Fine Pitch Ball Grid Array (FBGA)
676
3.2
16.4
13.0
12.0
°C/W
Fine Pitch Ball Grid Array (FBGA)
896
2.4
13.6
10.4
9.4
°C/W
Fine Pitch Ball Grid Array (FBGA)
1152
1.8
12.0
8.9
7.9
°C/W
Ceramic Quad Flat Pack (CQFP)1
208
2.0
22
19.8
18.0
°C/W
Ceramic Quad Flat Pack (CQFP)1
352
2.0
17.9
16.1
14.7
°C/W
Ceramic Column Grid Array (CCGA)2
624
6.5
8.9
8.5
8
°C/W
Notes:
1.
θjc for the 208-pin and 352-pin CQFP refers to the thermal resistance between the junction and the bottom of the package.
2.
θjc for the 624-pin CCGA refers to the thermal resistance between the junction and the top surface of the package. Thermal
resistance from junction to board (
θ
jb) for CCGA 624 package is 3.4°C/W.
Maximum Power Allowed
Max. junction temp. (
°C) Max. ambient temp. (°C)
–
θ
ja(°C/W)
---------------------------------------------------------------------------------------------------------------------------------------
125
°C70°C
–
13.6
°C/W
------------------------------------
4.04 W
=