M1AFS600-PQ208 Datasheet, PDF (258/334 Pages) Microsemi Corporation – Fusion Family of Mixed Signal FPGAs

DC and Power Characteristics
Theta-JA
Junction-to-ambient thermal resistance (_JA) is determined under standard conditions specified by
JEDEC (JESD-51), but it has little relevance in actual performance of the product. It should be used with
caution but is useful for comparing the thermal performance of one package to another.
A sample calculation showing the maximum power dissipation allowed for the AFS600-FG484 package
under forced convection of 1.0 m/s and 75°C ambient temperature is as follows:
Maximum Power Allowed = -^T---^J---⁽-^M----^A---^X---⁾---–-----^T----^A---⁽--^M---^A----^X---⁾
_JA
where
EQ 4
_JA = 19.00°C/W (taken from Table 3-6 on page 3-7).
T_A = 75.00°C
Maximum Power Allowed = ¹----⁰---⁰----^.-⁰¹----⁰⁹---^°.--_0C---₀---–_°---_C--⁷--_/-⁵-_W--^.--⁰---⁰----^°--^C--- = 1.3 W
EQ 5
The power consumption of a device can be calculated using the Microsemi power calculator. The
device's power consumption must be lower than the calculated maximum power dissipation by the
package. If the power consumption is higher than the device's maximum allowable power dissipation, a
heat sink can be attached on top of the case, or the airflow inside the system must be increased.
Theta-JB
Junction-to-board thermal resistance (_JB) measures the ability of the package to dissipate heat from the
surface of the chip to the PCB. As defined by the JEDEC (JESD-51) standard, the thermal resistance
from junction to board uses an isothermal ring cold plate zone concept. The ring cold plate is simply a
means to generate an isothermal boundary condition at the perimeter. The cold plate is mounted on a
JEDEC standard board with a minimum distance of 5.0 mm away from the package edge.
Theta-JC
Junction-to-case thermal resistance (_JC) measures the ability of a device to dissipate heat from the
surface of the chip to the top or bottom surface of the package. It is applicable for packages used with
external heat sinks. Constant temperature is applied to the surface in consideration and acts as a
boundary condition. This only applies to situations where all or nearly all of the heat is dissipated through
the surface in consideration.
Calculation for Heat Sink
For example, in a design implemented in an AFS600-FG484 package with 2.5 m/s airflow, the power
consumption value using the power calculator is 3.00 W. The user-dependent T_a and T_j are given as
follows:
T_J = 100.00°C
T_A = 70.00°C
From the datasheet:
_JA = 17.00°C/W
_JC = 8.28°C/W
P
=
-^T---^J----–-----^T----^A-
_JA
=
1_----0_---01_----°7_--C_{-.--0---–0----}7_-W---0_---°_--C_---
=
1.76 W
EQ 6
3-8
Revision 4