OR4 datasheet(143/152 Pages) LATTICE

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Lattice Semiconductor

143

Data Sheet

May, 2006

ORCA Series 4 FPGAs

ΘJC

This is the thermal resistance from junction to case. It is most often used when attaching a heat sink to the top of

the package. It is defined by:

The parameters in this equation have been defined above. However, the measurements are performed with the

case of the part pressed against a water-cooled heat sink to draw most of the heat generated by the chip out the

top of the package. It is this difference in the measurement process that differentiates ΘJC from ψJC. ΘJC is a true

thermal resistance and is expressed in units of °C/W.

ΘJB

This is the thermal resistance from junction to board (ΘJL). It is defined by:

where TB is the temperature of the board adjacent to a lead measured with a thermocouple. The other parameters

on the right-hand side have been defined above. This is considered a true thermal resistance, and the measure-

ment is made with a water-cooled heat sink pressed against the board to draw most of the heat out of the leads.

Note that ΘJB is expressed in units of °C/W, and that this parameter and the way it is measured are still in JEDEC

committee.

ΘJC

–

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ΘJB

–

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OR4 Datasheet(PDF) 143 Page - Lattice Semiconductor