Actel Fusion Mixed-Signal FPGAs
Pr el iminar y v1 .7
3-9
The 2.35 W power is less than the required 3.00 W. The design therefore requires a heat sink, or the
airflow where the device is mounted should be increased. The design's total junction-to-air thermal
resistance requirement can be estimated by
EQ 3-6:
EQ 3-6
Determining the heat sink's thermal performance proceeds as follows:
EQ 3-7
where
EQ 3-8
A heat sink with a thermal resistance of 5.01°C/W or better should be used. Thermal resistance of
heat sinks is a function of airflow. The heat sink performance can be significantly improved with
increased airflow.
Carefully estimating thermal resistance is important in the long-term reliability of an Actel FPGA.
Design engineers should always correlate the power consumption of the device with the maximum
allowable power dissipation of the package selected for that device.
Note: The junction-to-air and junction-to-board thermal resistances are based on JEDEC standard
(JESD-51) and assumptions made in building the model. It may not be realized in actual application
and therefore should be used with a degree of caution. Junction-to-case thermal resistance
assumes that all power is dissipated through the case.
Temperature and Voltage Derating Factors
θ
JA
=
0.37°C/W
=
Thermal resistance of the interface material
between the case and the heat sink, usually
provided by the thermal interface manufacturer
θ
SA
=
Thermal resistance of the heat sink in °C/W
Table 3-7
Temperature and Voltage Derating Factors for Timing Delays
(normalized to TJ = 70°C, VCC = 1.425 V)
Array
Voltage VCC
(V)
Junction Temperature (°C)
–40°C
0°C
25°C
70°C
85°C
110°C
1.425
0.88
0.93
0.95
1.00
1.02
1.05
1.500
0.83
0.88
0.90
0.95
0.96
0.99
1.575
0.80
0.85
0.87
0.91
0.93
0.96
θ
ja(total)
T
J
T
A
–
P
-----------------
110°C
70°C
–
3.00 W
-----------------------------------
13.33°C/W
==
=
θ
JA(TOTAL)
θ
JC
θ
CS
θ
SA
++
=
θ
SA
θ
JA(TOTAL)
θ
JC
–
θ
CS
–
=
θ
SA
13.33°C/W
8.28°C/W
–
0.37°C/W
–
5.01°C/W
==