40MX and 42MX FPGA Families
1- 22
v6.1
Junction Temperature (TJ)
The temperature variable in the Designer software refers
to
the
junction
temperature,
not
the
ambient
temperature. This is an important distinction because the
heat generated from dynamic power consumption is
usually hotter than the ambient temperature.
EQ 1-1,shown below, can be used to calculate junction
temperature.
EQ 1-1
Junction Temperature =
ΔT + T
a(1)
Where:
Ta = Ambient Temperature
ΔT = Temperature gradient between junction (silicon)
and ambient
ΔT = θ
ja * P(2)
P = Power
θ
ja = Junction to ambient of package. θja numbers are
located in the Package Thermal Characteristics table
below.
Package Thermal Characteristics
The device junction-to-case thermal characteristic is
θ
jc,
and the junction-to-ambient air characteristic is
θ
ja. The
thermal characteristics for
θ
ja are shown with two
different air flow rates.
The maximum junction temperature is 150
°C.
Maximum
power
dissipation
for
commercial-
and
industrial-grade devices is a function of θja.
A sample calculation of the absolute maximum power
dissipation allowed for a TQFP 176-pin package at
commercial temperature and still air is as follow:
The maximum power dissipation for military-grade devices is a function of θjc. A sample calculation of the absolute
maximum power dissipation allowed for CQFP 208-pin package at military temperature and still air is as follows:
Table 21
Package Thermal Characteristics
Plastic Packages
Pin Count
θ
jc
θ
ja
Units
Still Air
1.0 m/s
200 ft/min.
2.5 m/s
500 ft/min.
Plastic Quad Flat Pack
100
12.0
27.8
23.4
21.2
°C/W
Plastic Quad Flat Pack
160
10.0
26.2
22.8
21.1
°C/W
Plastic Quad Flat Pack
208
8.0
26.1
22.5
20.8
°C/W
Plastic Quad Flat Pack
240
8.5
25.6
22.3
20.8
°C/W
Plastic Leaded Chip Carrier
44
16.0
20.0
24.5
22.0
°C/W
Plastic Leaded Chip Carrier
68
13.0
25.0
21.0
19.4
°C/W
Plastic Leaded Chip Carrier
84
12.0
22.5
18.9
17.6
°C/W
Thin Plastic Quad Flat Pack
176
11.0
24.7
19.9
18.0
°C/W
Very Thin Plastic Quad Flat Pack
80
12.0
38.2
31.9
29.4
°C/W
Very Thin Plastic Quad Flat Pack
100
10.0
35.3
29.4
27.1
°C/W
Plastic Ball Grid Array
272
3.0
18.3
14.9
13.9
°C/W
Ceramic Packages
Ceramic Quad Flat Pack
208
2.0
22.0
19.8
18.0
°C/W
Ceramic Quad Flat Pack
256
2.0
20.0
16.5
15.0
°C/W
Maximum Power Allowed
Max. junction temp. (
°C) Max. ambient temp. (°C)
–
θ
ja(°C/W)
---------------------------------------------------------------------------------------------------------------------------------
150
°C70°C
–
28
°C/W
-----------------------------------
2.86W
=
Maximum Power Allowed
Max. junction temp. (
°C) Max. ambient temp. (°C)
–
θ
jc(°C/W)
---------------------------------------------------------------------------------------------------------------------------------
150
°C 125°C
–
6.3
°C/W
--------------------------------------
3.97W
=