Datasheet

732
32133D–11/2011
UC3D
33. Mechanical Characteristics
33.1 Thermal Considerations
33.1.1 Thermal Data
Table 33-1 summarizes the thermal resistance data depending on the package.
33.1.2 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 33-1.
• θ
JC
= package thermal resistance, Junction-to-case thermal resistance (°C/W), provided in
Table 33-1.
• 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 32.5 on
page 717.
•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 33-1. Thermal Resistance Data
Symbol Parameter Condition Package Typ Unit
θ
JA
Junction-to-ambient thermal resistance Still Air TQFP48 65.1
⋅C/W
θ
JC
Junction-to-case thermal resistance TQFP48 23.4
θ
JA
Junction-to-ambient thermal resistance Still Air QFN48 29.2
⋅C/W
θ
JC
Junction-to-case thermal resistance QFN48 2.7
θ
JA
Junction-to-ambient thermal resistance Still Air TQFP64 63.1
⋅C/W
θ
JC
Junction-to-case thermal resistance TQFP64 23.0
θ
JA
Junction-to-ambient thermal resistance Still Air QFN64 26.9
⋅C/W
θ
JC
Junction-to-case thermal resistance QFN64 2.7
T
J
T
A
P
D
θ
JA
×()+=
T
J
T
A
P(
D
θ(
HEATSINK
×θ
JC
))++=