
RadTolerant FPGAs
1- 8
v3.1
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.
Maximum junction temperature is 150°C.
A sample calculation of the absolute maximum power
dissipation allowed for a CQFP 172-pin package at
military temperature is as follows:
EQ 1-2
Power Dissipation
General Power Equation
P = [ICCstandby + ICCactive] * VCC + IOL * VOL * N +
IOH * (VCC – VOH) * M
EQ 1-3
where:
ICCstandby is the current flowing when no inputs
or outputs are changing.
ICCactive is the current flowing due to CMOS
switching.
IOL, IOH are TTL sink/source currents.
VOL, VOH are TTL level output voltages.
N equals the number of outputs driving TTL loads
to VOL.
M equals the number of outputs driving TTL loads
to VOH.
Accurate values for N and M are difficult to determine
because they depend on the family type, on design
details, and on the system I/O. The power can be divided
into two components: static and active.
Static Power Component
Actel FPGAs have small static power components that
result in power dissipation lower than that of PALs or
PLDs. By integrating multiple PALs or PLDs into one
FPGA, an even greater reduction in board-level power
dissipation can be achieved.
The power due to standby current is typically a small
component of the overall power. Standby power is
calculated below for commercial, worst-case conditions.
The static power dissipated by TTL loads depends on the
number of outputs driving HIGH or LOW and on the DC
load current. Again, this value is typically small. For
instance, a 32-bit bus sinking 4 mA at 0.33 V will
generate 42 mW with all outputs driving LOW, and
140 mW with all outputs driving HIGH.
Table 1-6 Package Thermal Characteristics
Package Type
Pin Count
θ
jc
θ
ja
Still Air
θ
ja
300 ft./min.
Units
Ceramic Quad Flat Pack
8
7.8
40
30
°C/W
132
7.2
35
25
°C/W
172
6.8
25
20
°C/W
196
6.4
23
15
°C/W
256
6.2
20
10
°C/W
Max. junction temp. (°C) – Max. military temp.
θ
ja
°C/W
()
-----------------------------------------------------------------------------------------------------------------------
150°C – 125°C
25°C/W
---------------------------------------1.0W
==
ICC
VCC
Power
2 mA
5.25 V
10.5 mW