TS68040 ATMEL Corporation, TS68040 Datasheet - Page 11

• Manufacturer Part Number: TS68040
• Description: 32-bit Mpu, 25-33 MHZ
• Manufacturer: ATMEL Corporation

Relationships between thermal resistances and temperatures
Since the maximum operating junction temperature has been specified to be 125°C. The maximum case temperature, T C ,
in °C can be obtained from :
where :
T C
T J
P D
In general, the ambient temperature, T A , in °C is a function of the following formula :
Where the thermal resistance from case to ambient,
configuration has been determined. As seen from equation (4.3), reducing the case to ambient thermal resistance increases
the maximum operating ambient temperature. Therefore, by utilizing such methods as heat sinks and ambient air cooling to
minimize the
However, an easier approach to thermal evaluation uses the following formulas :
or alternatively,
where :
This total thermal resistance of a package,
represent the barrier to heat flow from the semiconductor junction to the package (case) surface ( JC ) and from the case
to the outside ambient ( JC ). Although
Thus, good thermal management by the user can significantly reduce
temperature or a higher ambient operating temperature.
Thermal management techniques
To attain a reasonable maximum ambient operating temperature, a user must reduce the barrier to heat flow from the
semiconductor junction to the outside ambient ( JA ). The only way to accomplish this is to significantly reduce
applying such thermal management techniques as heat sinks and ambient air cooling.
The following paragraphs discuss some results of a thermal study of the TS 68040 device without using any thermal mana-
gement techniques ; using only air-flow cooling, using only a heat sink, and using heat sink combined with air-flow cooling.
Thermal characteristics in still air
A sample size of three TS 68040 packages was tested in free-air cooling with no heat sink. Measurements showed that the
average
from within the package. The test determined that
possible. Therefore, since the variance in
for calculation purposes that
results of a maximum power dissipation of 3 and 5 W with no heat sink or air-flow (refer to Table 6 to calculate other power
dissipation values).
Table 7 - Thermal parameters with no heat sink or air-flow
As seen by looking at the ambient temperature results, most users will want to implement some type of thermal management
to obtain a more reasonable maximum ambient temperature.
Thermal characteristics in forced air
A sample size of three TS 68040 packages was tested in forced air cooling in a wind tunnel with no heat sink. This test
was performed with 3 W of power being dissipated from within the package. As previously mentioned, since the variance in
power levels. Using the previous formulas, Table 8 shows the results of the maximum power dissipation at 3 and 5 W with
air-flow and no heat sink (refer to Table 6 to calculate other power dissipation values).
JC
JA = thermal resistance from the junction to the ambient ( JC +
JA within the possible power range is negligible, it can be assumed for calculation purposes that
3 Watts
5 Watts
P D
JA was 22.8°C/W with a standard deviation of 0.44°C/W. The test was performed with 3 W of power being dissipated
= Maximum case temperature
= Maximum junction temperature
= Maximum power dissipation of the device
= Thermal resistance between the junction of the die and the case
CA , a higher ambient operating temperature and / or a lower junction temperature can be achieved.
Defined paramaters
125°C
125°C
T J
JA is valid at all power levels. Using the formulas introduced previously, Table 7 shows the
JC is device related and cannot be influenced by the user,
1°C/W
1°C/W
JC
JA within the possible power dissipation range is negligible, it can be assumed
T A
JA , is a combination of its two components,
T J – P D
T C
T A
T J
JA will decrease slightly for the increasing power dissipation range
T A
T J – P D
T J – P D
Measured
21.8°C/W
21.8°C/W
CA , is the only user-dependent parameter once a buffer output
P D
JC – P D
JA
JC
JA
JA
CA ).
CA achieving either a lower semiconductor junction
CA
20.8°C/W
20.8°C/W
JA
CA
– JC
T
JC and
Calculated
J
–
122°C
120°C
T C
P
D
CA . These components
CA is user dependent.
JC
JA is constant at all
(Equation 4.2)
(Equation 4.3)
(Equation 4.4)
(Equation 4.5)
T
J
59.6°C
–
16°C
T A
P
D
CA by
11/38
JA