Datasheet

Appendix A Electrical Characteristics
MC9S12XE-Family Reference Manual Rev. 1.25
Freescale Semiconductor 1207
A.1.8 Power Dissipation and Thermal Characteristics
Power dissipation and thermal characteristics are closely related. The user must assure that the maximum
operating junction temperature is not exceeded. The average chip-junction temperature (T
J
) in °C can be
obtained from:
The total power dissipation can be calculated from:
P
IO
is the sum of all output currents on I/O ports associated with V
DDX
, whereby
Two cases with internal voltage regulator enabled and disabled must be considered:
1. Internal voltage regulator disabled
2. Internal voltage regulator enabled
T
J
T
A
P
D
Θ
JA
•()+=
T
J
Junction Temperature, [°C ]=
T
A
Ambient Temperature, [°C ]=
P
D
Total Chip Power Dissipation, [W]=
Θ
JA
Package Thermal Resistance, [°C/W]=
P
D
P
INT
P
IO
+=
P
INT
Chip Internal Power Dissipation, [W]=
P
IO
R
DSON
i
∑
I
IO
i
2
⋅=
R
DSON
V
OL
I
OL
------------ for outputs driven low;=
R
DSON
V
DD35
V
OH
–
I
OH
--------------------------------------- for outputs driven high;=
P
INT
I
DD
V
DD
⋅ I
DDPLL
V
DDPLL
⋅ I
DDA
+V
DDA
⋅+=
P
INT
I
DDR
V
DDR
⋅ I
DDA
V
DDA
⋅+=