Datasheet

Appendix A Electrical Characteristics and Timing Specifications
MC9S08AC16 Series Data Sheet, Rev. 9
Freescale Semiconductor 295
V
DD
and multiply by the pin current for each I/O pin. Except in cases of unusually high pin current (heavy
loads), the difference between pin voltage and V
SS
or V
DD
will be very small.
The average chip-junction temperature (T
J
) in C can be obtained from:
T
J
= T
A
+ (P
D
 
JA
) Eqn. A-1
where:
T
A
= Ambient temperature, C

JA
= Package thermal resistance, junction-to-ambient, C/W
P
D
= P
int
P
I/O
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 equations 1 and 2 for K gives:
K = P
D
 (T
A
+ 273C) + 
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 equations 1 and 2 iteratively for any value of T
A
.
Table A-3. Thermal Characteristics
Rating Symbol Value Unit
Operating temperature range (packaged)
T
A
T
L
to T
H
–40 to 125
C
Thermal resistance
1,2,3,4
1
Junction temperature is a function of die size, on-chip power dissipation, package thermal
resistance, mounting site (board) temperature, ambient temperature, air flow, power
dissipation of other components on the board, and board thermal resistance.
2
Junction to Ambient Natural Convection
3
1s - Single Layer Board, one signal layer
4
2s2p - Four Layer Board, 2 signal and 2 power layers

JA
C/W
48-pin QFN 1s
2s2p
84
27
44-pin LQFP 1s
2s2p
73
56
32-pin LQFP 1s
2s2p
85
56
42-pin SDIP 1s
2s2p
58
47