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TS68C429AVR1B View Datasheet(PDF) - Atmel Corporation

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TS68C429AVR1B Datasheet PDF : 43 Pages
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Power Considerations
Mechanical and
Environment
Marking
TS68C429A
The average chip-junction temperature, TJ, in °C can be obtained from:
TJ = TA + (PD ⋅ θJA)
(1)
TA = Ambient Temperature, °C
θJA = Package Thermal Resistance, Junction-to-Ambient, °C/W
PD = PINT + PI/O
PINT = ICC x VCC, Watts—Chip Internal Power
PI/O = Power Dissipation on Input and Output Pins—User Determined
For most applications PI/O < PINT and can be neglected.
An approximate relationship between PD and TJ (if PI/O is neglected) is:
PD = K: (TJ + 273)
(2)
Solving equations (1) and (2) for K gives:
K = PD (TA + 273) + θJA PD2
(3)
where K is a constant pertaining to the particular part K can be determined from equa-
tion (3) by measuring PD (at equilibrium) for a known TA. Using this value of K, the
values of PD and TJ can be obtained by solving equations (1) and (2) iteratively for any
value of TA.
The total thermal resistance of a package (θJA) can be separated into two components,
θJC and θCA, representing the barrier to heat flow from the semiconductor junction to the
package (case), surface (θJC) and from the case to the outside ambient (θCA). These
terms are related by the equation:
θJA = θJC + θCA
(4)
θJC is device related and cannot be influenced by the user. However, θCA is user depen-
dent and can be minimized by such thermal management techniques as heat sinks,
ambient air cooling and thermal convection. Thus, good thermal management on the
part of the user can significantly reduce θCA so that θJA approximately equals θJC. Substi-
tution of θJC for θJA in equation (1) will result in a lower semiconductor junction
temperature.
The microcircuits shall meet all mechanical environmental requirements of either MIL-
STD-883 for class B devices or DESC devices.
The document where are defined the marking are identified in the related reference doc-
uments. Each microcircuit are legibly and permanently marked with the following
information as minimum:
• Atmel logo
• Manufacturer’s part number
• Class B identification
• Date-code of inspection lot
• ESD identifier if available
• Country of manufacturing
9
2120A–HIREL–08/02
 

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