Datasheet

Appendix A Electrical Characteristics
MC9S08LC60 Series Data Sheet: Technical Data, Rev. 4
324 Freescale Semiconductor
A.3 Thermal Characteristics
This section provides information about operating temperature range, power dissipation, and package
thermal resistance. Power dissipation on I/O pins is usually small compared to the power dissipation in
on-chip logic and voltage regulator circuits and it is user-determined rather than being controlled by the
MCU design. In order to take P
I/O
into account in power calculations, determine the difference between
actual pin voltage and V
SS
or 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
×θ
JA
) Eqn. A-1
where:
T
A
= Ambient temperature, °C
θ
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 Equation A-1 and Equation A-2 for K gives:
Table A-2. Thermal Characteristics
Rating Symbol Value Unit
Operating temperature range (packaged)
T
A
-40 to 85 °C
Thermal resistance
80-pin LQFP
1s
2s2p
64-pin LQFP
1s
2s2p
θ
JA
(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, airflow, 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
64
49
66
47
°C/W