Sun Microsystems SME5224AUPA-400 - Manual (Page 47)

19
400 MHz CPU, 4.0 MB E-Cache
UltraSPARC ™ -II CPU Module
SME5224AUPA-400
Advanced Version
July 1999 Sun Microsystems, Inc
Thermal Definitions and Specifications
Term Definition Specification Comments
Tj Maximum device
junction
temperature 85
°
C, The Tj can't be measured directly by a thermo-couple
probe. It must always be estimated as Tj or less. Less is
preferred.
Tc Maximum case
temperature 76.7
°
C Measurable at the top-center of the device. Requires a hole
in the base of the heatsink to allow the thermocouple to be
in contact with the case. Maximum case temperature is
specified using a CPU device at its maximum power
dissipation.
Ts Heatsink
temperature 75
°
C Measurable at the temperature of the base of the heatsink.
The best approach is to embed a thermocouple in a cavity
drilled in the heatsink base. An alternative approach is to
place the thermocouple between the fins/pins of the heat-
sink (insulated from the airflow) and in contact with the
base plate of the heatsink.
Ta Module ambient air
temperature see page 20 The air temperature as it approaches the heatsink.
Pd Typical power
dissipation of the
CPU 19.0 W The worst case compute loads over the entire process
range.
θ
jc Maximum
junction-to-case
thermal resistance
of the package 0.5
°
C/W The specification for the UltraSPARC™–II, 400 MHz CPU
in a ceramic LGA package.
θ
cs Case-to-heatsink
thermal resistance 0.1
°
C/W Accuracy of this value requires that good thermal contact is
made between the package and the heatsink.
θ
sa Heatsink-to-air
thermal resistance see page 20 This value is dependent on the heatsink design, the airflow
direction, and the airflow velocity.
Va Air velocity see page 20 The ducted airflow.