Datasheet

931
32142D–06/2013
ATUC64/128/256L3/4U
36. Mechanical Characteristics
36.1 Thermal Considerations
36.1.1 Thermal Data
Table 36-1 summarizes the thermal resistance data depending on the package.
36.1.2 Junction Temperature
The average chip-junction temperature, T
J
, in °C can be obtained from the following:
1.
2.
where:
• 
JA
= package thermal resistance, Junction-to-ambient (°C/W), provided in Table 36-1.
• 
JC
= package thermal resistance, Junction-to-case thermal resistance (°C/W), provided in
Table 36-1.
• 
HEAT SINK
= cooling device thermal resistance (°C/W), provided in the device datasheet.
•P
D
= device power consumption (W) estimated from data provided in Section 35.4 on page
898.
•T
A
= ambient temperature (°C).
From the first equation, the user can derive the estimated lifetime of the chip and decide if a
cooling device is necessary or not. If a cooling device is to be fitted on the chip, the second
equation should be used to compute the resulting average chip-junction temperature T
J
in °C.
Table 36-1. Thermal Resistance Data
Symbol Parameter Condition Package Typ Unit

JA
Junction-to-ambient thermal resistance Still Air TQFP48 54.4
C/W

JC
Junction-to-case thermal resistance TQFP48 15.7

JA
Junction-to-ambient thermal resistance Still Air QFN48 26.0
C/W

JC
Junction-to-case thermal resistance QFN48 1.6

JA
Junction-to-ambient thermal resistance Still Air TLLGA48 25.4
C/W

JC
Junction-to-case thermal resistance TLLGA48 12.7

JA
Junction-to-ambient thermal resistance Still Air TQFP64 52.9
C/W

JC
Junction-to-case thermal resistance TQFP64 15.5

JA
Junction-to-ambient thermal resistance Still Air QFN64 22.9
C/W

JC
Junction-to-case thermal resistance QFN64 1.6
T
J
T
A
P
D

JA
+=
T
J
T
A
P
D

HEATSINK

JC
++=