FG256 datasheet(21/197 Pages) MICROSEMI

21 / 197 page

SmartFusion Customizable System-on-Chip (cSoC)

Re vi s i on 12

2 - 9

EQ 6

The 1.76 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 7:

EQ 7

Determining the heat sink's thermal performance proceeds as follows:

EQ 8

where

EQ 9

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 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

θJA = 0.37°C/W

= Thermal resistance of the interface material between

the case and the heat sink, usually provided by the

thermal interface manufacturer

θSA = Thermal resistance of the heat sink in °C/W

Table 2-7 • Temperature and Voltage Derating Factors for Timing Delays

(normalized to TJ = 85°C, worst-case VCC = 1.425 V)

Array

Voltage VCC

(V)

Junction Temperature (°C)

–40°C

0°C

25°C

70°C

85°C

100°C

1.425

0.86

0.91

0.93

0.98

1.00

1.02

1.500

0.81

0.86

0.88

0.93

0.95

0.96

1.575

0.78

0.83

0.85

0.90

0.91

0.93

TJ TA

–

θJA

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

100°C 70°C

–

17.00 W

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

1.76 W

θJA(total)

TJ TA

–

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

100°C 70°C

–

3.00 W

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

10.00°C/W

θJA(TOTAL)

θJC θCS θSA

θSA

θJA(TOTAL) θJC

–

θCS

–

θSA

13.33°C/W 8.28°C/W

–

0.37°C/W

–

5.01°C/W

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