U1AFS250-FG256 Datasheet, PDF (9/27 Pages) Actel Corporation – 3 - DC and Power Characteristics

Actel Fusion Mixed-Signal FPGA for the MicroBlade AdvancedMC Solution
The 1.70 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:
θ_ja(total)
=
-^T---^J---^–----^T---^A--
P
=
1_----1_---0_----°_--C_-----–_-----7_---0_----°_--C_--
3.00 W
=
13.33°C/W
Determining the heat sink's thermal performance proceeds as follows:
θ_JA(TOTAL) = θ_JC + θ_CS + θ_SA
EQ 3-6
where
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
EQ 3-7
θ_SA = θ_JA(TOTAL) – θ_JC – θ_CS
θ_SA = 13.33°C/W – 6.80°C/W – 0.37°C/W = 6.16°C^·/W
EQ 3-8
A heat sink with a thermal resistance of 6.16°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
Table 3-7 • Temperature and Voltage Derating Factors for Timing Delays
(normalized to T_J = 70°C, V_CC = 1.425 V)
Array
Voltage V_CC
(V)
–40°C
Junction Temperature (°C)
0°C
25°C
70°C
85°C
1.425
0.88
0.93
0.95
1.00
1.02
1.500
0.83
0.88
0.90
0.95
0.96
1.575
0.80
0.85
0.87
0.91
0.93
110°C
1.05
0.99
0.96
Preliminary v0.4
3-9