Rainbow Electronics AT91CAP9S250A - Manual (Page 988)

988
6264A–CAP–21-May-07
AT91CAP9S500A/AT91CAP9S250A
48. AT91CAP9 Mechanical Characteristics
48.1 Thermal Considerations
48.1.1 Thermal Data
Table 48-1 summarizes the thermal resistance data depending on the package.
48.1.2 Junction Temperature
The average chip-junction temperature, T
J
, in °C can be obtained from the following:
3.
4.
where:
•
θ
JA
= package thermal resistance, Junction-to-ambient (°C/W), provided in Table 48-1 on
page 988 .
•
θ
JC
= package thermal resistance, Junction-to-case thermal resistance (°C/W), provided in
Table 48-1 on page 988 .
•
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 Section 47.3
”Power Consumption” on page 960 .
• 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 48-1. Thermal Resistance Data
Symbol Parameter Condition Package Typ Unit
θ
JA
Junction-to-ambient thermal resistance Still Air
TFBGA
400
°C/W
θ
JC
Junction-to-case thermal resistance Still Air
TFBGA
400
°C/W
T
J
T
A
P
D
θ
JA
× ( )
+ =
T
J
T
A
P
(
D
θ (
HEATSINK
× θ
JC
) )
+ + =