4-1
Chapter 4
Design
Considerations
4.1 Thermal Design Considerations
The average chip-junction temperature
,
T
J
,
in
°
C can be obtained from the following:
Equation 1:
T
J
= T
A
+ (P
D
•
θ
JA
)
where
T
A
= ambient temperature
°
C
θ
JA
= package thermal resistance
,
junction to ambient
,
°
C/W
P
D
= P
INT
+ P
I/O
in W
P
INT
= I
DD
×
V
DD
in W—chip internal power
P
I/O
= power dissipation on output pins in W—user determined
The user should set T
A
and P
D
such that T
J
does not exceed the maximum operating conditions. In case
T
J
is too high, the user should either lower the ambient temperature or the power dissipation of the chip.