FG896 datasheet(19/162 Pages) MICROSEMI

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ProASIC3E Flash Family FPGAs

Revision 13

2-5

Thermal Characteristics

Introduction

The temperature variable in 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 to be higher than the ambient temperature.

EQ 1 can be used to calculate junction temperature.

TJ = Junction Temperature = T + TA

EQ 1

where:

TA = Ambient Temperature

T = Temperature gradient between junction (silicon) and ambient T = ja * P

ja = Junction-to-ambient of the package. ja numbers are located in Table 2-5.

P = Power dissipation

Package Thermal Characteristics

The device junction-to-case thermal resistivity is

jc and the junction-to-ambient air thermal resistivity is

ja. The thermal characteristics for ja are shown for two air flow rates. The absolute maximum junction

temperature is 110°C. EQ 2 shows a sample calculation of the absolute maximum power dissipation

allowed for an 896-pin FBGA package at commercial temperature and in still air.

EQ 2

Temperature and Voltage Derating Factors

Maximum Power Allowed

Max. junction temp. (

C) Max. ambient temp. (C)

–



ja(C/W)

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

110

C70C

–

13.6

C/W

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

5.88 W

Table 2-5 • Package Thermal Resistivities

Package Type

Pin Count

jc

ja

Units

Still Air

200 ft./min.

500 ft./min.

Plastic Quad Flat Package (PQFP)

208

8.0

26.1

22.5

20.8

C/W

Plastic Quad Flat Package (PQFP) with

embedded heat spreader

208

3.8

16.2

13.3

11.9

C/W

Fine Pitch Ball Grid Array (FBGA)

256

3.8

26.9

22.8

21.5

C/W

484

3.2

20.5

17.0

15.9

C/W

676

3.2

16.4

13.0

12.0

C/W

896

2.4

13.6

10.4

9.4

C/W

Table 2-6 • 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

100°C

1.425

0.87

0.92

0.95

1.00

1.02

1.04

1.500

0.83

0.88

0.90

0.95

0.97

0.98

1.575

0.80

0.85

0.87

0.92

0.93

0.95

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