ort8850 Lattice Semiconductor Corp., ort8850 Datasheet - Page 100

• Manufacturer Part Number: ort8850
• Description: Field-programmable System Chip Fpsc Eight-channel X 850 Mbits/s Backplane Transceiver
• Manufacturer: Lattice Semiconductor Corp.

Lattice Semiconductor
Package Thermal Characteristics Summary
There are three thermal parameters that are in common use: θ
eters 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 T
Experimentally, θJA is determined when a special thermal 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 con-
vection measurements. A controlled amount of power (Q) is dissipated in the test chip’s heater resistor, the chip’s
temperature (T
that θ
ΨJC
This JEDEC designated parameter correlates the junction 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 T
ing the θ
reading, T
°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 θ
thermal resistance and is expressed in units of °C/W.
θJB
This is the thermal resistance from junction to board (Θ
where T
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 θ
cussed by the JEDEC committee.
JA
J
C
B
is expressed in units of °C/watt.
JA
is the junction temperature, T
is the temperature of the board adjacent to a lead measured with a thermocouple. The other parameters
is the case temperature at top dead center, T
C
JB
, is made with a thermocouple attached at top-dead-center of the case. ψ
measurements described above, besides the other parameters measured, an additional temperature
is expressed in units of °C/W and that this parameter and the way it is measured are still being dis-
J
) is determined by the forward drop on the diodes, and the ambient temperature (T
A,
is the ambient air temperature, and Q is the chip power.
Ψ
θ
θ
θ
JA
JC
JB
JC
=
=
=
=
JL
J
100
is the junction temperature, and Q is the chip power. Dur-
). It is defined by:
T
T
T
T
J
J
J
J
Q
Q
Q
- T
- T
- T
Q
- T
JA
C
B
A
C
,
ψ
JC
, and
θ
JC
. It should be noted that all the param-
ORCA ORT8850 Data Sheet
JC
is also expressed in units of
JC
from ψ
A
JC.
) is noted. Note
θ
JC
is a true
(1)
(2)
(3)
(4)