mc68hc901fn Freescale Semiconductor, Inc, mc68hc901fn Datasheet - Page 55

• Manufacturer Part Number: mc68hc901fn
• Description: Multi-function Peripheral
• Manufacturer: Freescale Semiconductor, Inc

Electrical Characteristics
8.3 POWER CONSIDERATIONS
The average chip-junction temperature, T
where:
For most applications P
An appropriate relationship between P
Solving equations (1) and (2) for K gives:
where K is a constant pertaining to the particular part. K can be determined from equation
(3) by measuring P
and T
The total thermal resistance of a package (
and
package (case) surface (
are related by the equation:
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
in equation (1) will result in a lower semiconductor junction temperature.
8-2
JC
is device related and cannot be influenced by the user. However,
T
T
P
P
P
P
K = P
CA
JA
JA
J
J
A
D
INT
I/O
D
can be obtained by solving equations (1) and (2) iteratively for any value of T
= T
= K
, representing the barrier to heat flow from the semiconductor junction to the
=
D
A
JC
• (T
= Ambient Temperature,
= Package Thermal Resistance, Junction-to-Ambient,
= P
= I
= Power Dissipation on Input and Output Pins, Watts — User Determined
+ (P
(T
+
CC
A
INT
J
D
+ 273
CA
+ 273
x V
•
D
+ P
(at equilibrium) for a known T
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (4)
JA
CC
I/O
) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (1)
I/O
˚
, Watts — Chip Internal Power
˚
C) +
C) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (2)
CA
JC
< P
so that
) and from the case to the outside ambient (
INT
JA
MC68HC901 USER’S MANUAL
• P
and can be neglected.
JA
D
˚
2
D
C
approximately equals
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (3)
and T
J
, in
JA
) can be separated into two components,
˚
J
C can be obtained from:
(if P
A
. Using this value of K, the values of P
I/O
is neglected) is:
JC
. Substitution of
˚
C/W
CA
is user dependent
CA
). These terms
MOTOROLA
JC
for
A
.
JC
JA
D