OR3LP26B datasheet(178/184 Pages) AGERE

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178

Lucent Technologies Inc.

ORCA OR3LP26B FPSC

Data Sheet

Embedded Master/Target PCI Interface

March 2000

Lucent Technologies Inc.

Package Thermal Characteristics

Summary

There are three thermal parameters that are in com-

mon use:

ΘJA, ψJC, and ΘJC. It should be noted that all

the parameters are affected, to varying degrees, by

package design (including paddle size) and choice of

materials, the amount of copper in the test board or

system board, and system airflow.

ΘJA

This is the thermal resistance from junction to ambient

(theta-JA, R-theta, etc.).

where TJ is the junction temperature, TA is the ambient

air temperature, and Q is the chip power.

Experimentally,

ΘJA is determined when a special ther-

mal test die is assembled into the package of interest,

and the part is mounted on the thermal test board. The

diodes on the test chip are separately calibrated in an

oven. The package/board is placed either in a JEDEC

natural convection box or in the wind tunnel, the latter

for forced convection measurements. A controlled

amount of power (Q) is dissipated in the test chip’s

heater resistor, the chip’s temperature (TJ) is deter-

mined by the forward drop on the diodes, and the ambi-

ent temperature (TA) is noted. Note that

ΘJA is

expressed in units of °C/W.

ψJC

This JEDEC designated parameter correlates the junc-

tion temperature to the case temperature. It is generally

used to infer the junction temperature while the device

is operating in the system. It is not considered a true

thermal resistance, and it is defined by:

where TC is the case temperature at top dead center,

TJ is the junction temperature, and Q is the chip power.

During the

ΘJA measurements described above,

besides the other parameters measured, an additional

temperature reading, TC, is made with a thermocouple

attached at top-dead-center of the case.

ψJC is also

expressed in units of °C/W.

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

JC.

ΘJC is a true thermal resistance and is expressed

in units of °C/W.

ΘJB

This is the thermal resistance from junction to board

(

ΘJB). It is defined by:

where TB is the temperature of the board adjacent to a

lead measured with a thermocouple. The other param-

eters on the right-hand side have been defined above.

This is considered a true thermal resistance, and the

measurement 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 mea-

sured are still in JEDEC committee.

FPGA Maximum Junction Temperature

Once the power dissipated by the FPGA has been

determined (see the Estimating Power Dissipation sec-

tion), the maximum junction temperature of the FPGA

can be found. This is needed to determine if speed der-

ating of the device from the 85 °C junction temperature

used in all of the delay tables is needed. Using the

maximum ambient temperature, TAmax, and the power

dissipated by the device, Q (expressed in °C), the max-

imum junction temperature is approximated by:

TJmax = TAmax + (Q •

ΘJA)

Table 71 lists the thermal characteristics for all pack-

ages used with the

ORCA OR3LP26B Series of

FPGAs.

ΘJA

–

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

ψJC

–

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

ΘJC

–

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

ΘJB

–

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

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