Technical Data
MC68HC908MR8 — Rev 4.1
342
Electrical Specifications
Freescale Semiconductor
Electrical Specifications
21.5 Thermal Characteristics
Characteristic
Symbol
Value
Unit
Thermal resistance
32-pin LQFP
28-pin PDIP
28-pin SOIC
θJA
68.9(1)
—
1. 32-pin LQFP resistance measured at 200 ft/min.
°C/W
I/O pin power dissipation
PI/O
User determined
W
Power dissipation(2)
2. Power dissipation is a function of temperature.
PD
PD = (IDD x VDD)
+ PI/O = K/(TJ + 273°C)
W
Constant(3)
3. K is a constant unique to the device. K can be determined for a known TA and measured
PD. With this value of K, PD and TJ can be determined for any value of TA.
K
PD x (TA + 273°C)
+ PD2 x θJA
W/
°C
Average junction temperature
TJ
TA + (PD x θJA)
°C
Maximum junction temperature
TJM
125
°C