Datasheet

Appendix A Electrical Characteristics
MC9S08QG8 and MC9S08QG4 Data Sheet, Rev. 5
Freescale Semiconductor 267
P
int
= I
DD
× V
DD
, Watts — chip internal power
P
I/O
= Power dissipation on input and output pins — user determined
For most applications, P
I/O
<< P
int
and can be neglected. An approximate relationship between P
D
and T
J
(if P
I/O
is neglected) is:
P
D
= K ÷ (T
J
+ 273°C) Eqn. A-2
Solving Equation A-1 and Equation A-2 for K gives:
K = P
D
× (T
A
+ 273°C) + θ
JA
× (P
D
)
2
Eqn. A-3
where K is a constant pertaining to the particular part. K can be determined from equation 3 by measuring
P
D
(at equilibrium) for a known T
A
. Using this value of K, the values of P
D
and T
J
can be obtained by
solving Equation A-1 and Equation A-2 iteratively for any value of T
A
.