
90
32117DS–AVR-01/12
AT32UC3C
8.
Mechanical Characteristics
8.1
Thermal Considerations
8.1.1
Thermal Data
Table 8-1 summarizes the thermal resistance data depending on the package.
8.1.2
Junction Temperature
The average chip-junction temperature, T
J, in °C can be obtained from the following:
1.
2.
where:
θ
JA = package thermal resistance, Junction-to-ambient (°C/W), provided in Table 8-1 on page θ
JC = package thermal resistance, Junction-to-case thermal resistance (°C/W), provided in
θ
HEAT SINK = cooling device thermal resistance (°C/W), provided in the device datasheet.
P
D = device power consumption (W) estimated from data provided in the section ”Power 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 8-1.
Thermal Resistance Data
Symbol
Parameter
Condition
Package
Typ
Unit
θ
JA
Junction-to-ambient thermal resistance
No air flow
QFN64
20.0
°C/W
θ
JC
Junction-to-case thermal resistance
QFN64
0.8
θ
JA
Junction-to-ambient thermal resistance
No air flow
TQFP64
40.5
°C/W
θ
JC
Junction-to-case thermal resistance
TQFP64
8.7
θ
JA
Junction-to-ambient thermal resistance
No air flow
TQFP100
39.3
°C/W
θ
JC
Junction-to-case thermal resistance
TQFP100
8.5
θ
JA
Junction-to-ambient thermal resistance
No air flow
LQFP144
38.1
°C/W
θ
JC
Junction-to-case thermal resistance
LQFP144
8.4
TJ
TA
PD θJA
×
()
+
=
TJ
TA
P
(
D
θ
(
HEATSINK
×θ
JC ))
++
=