AT32UC3B0512_1 Datasheet, PDF (633/676 Pages) ATMEL Corporation – 32-bit AVR® Microcontroller

AT32UC3B
29. Mechanical Characteristics
29.1 Thermal Considerations
29.1.1
Thermal Data
Table 29-1 summarizes the thermal resistance data depending on the package.
Table 29-1. Thermal Resistance Data
Symbol Parameter
Condition Package
Typ
θ_JA
Junction-to-ambient thermal resistance Still Air
TQFP64
49.6
θ_JC
Junction-to-case thermal resistance
TQFP64
13.5
θ_JA
Junction-to-ambient thermal resistance Still Air
TQFP48
51.1
θ_JC
Junction-to-case thermal resistance
TQFP48
13.7
Unit
⋅C/W
⋅C/W
29.1.2
Junction Temperature
The average chip-junction temperature, T_J, in °C can be obtained from the following:
1. T_J = T_A + (P_D × θ_JA)
2. T_J = T_A + (P _D × (θ _HEATSINK + θ_JC ) )
where:
• θ_JA = package thermal resistance, Junction-to-ambient (°C/W), provided in Table 29-1 on page
633.
• θ_JC = package thermal resistance, Junction-to-case thermal resistance (°C/W), provided in
Table 29-1 on page 633.
• 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
Consumption” on page 621.
• 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.
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