Philips Semiconductors Product data
AU5790Single wire CAN transceiver
2001 May 18
14
THERMAL CHARACTERISTICS
The AU5790 provides protection from thermal overload. When the
IC junction temperature reaches the threshold (≈155 °C), the
AU5790 will disable the transmitter drivers, reducing power
dissipation to protect the device. The transmit function will become
available again after the junction temperature drops. The thermal
shutdown hysteresis is about 5 °C.
In order to avoid this transmit function shutdown, care must be taken
to not overheat the IC during application. The relationships between
junction temperature, ambient temperature, dissipated power, and
thermal resistance can be expressed as:
T
j
=T
a
+ P
d
* θ
ja
where: T
j
is junction temperature (°C);
T
a
is ambient temperature (°C);
P
d
is dissipated power (W);
θ
ja
is thermal resistance (°C/W).
Thermal Resistance
Thermal resistance is the ability of a packaged IC to dissipate heat
to its environment. In semiconductor applications, it is highly
dependant on the IC package, PCBs, and airflow. Thermal
resistance also varies slightly with input power, the difference
between ambient and junction temperatures, and soldering material.
Figures 5 and 6 show the thermal resistance as the function of the
IC package and the PCB configuration, assuming no airflow.
SL01249
0
50
100
150
200
0 50 100 150 200 250
Thermal resistance (C/W)
Cu area on fused pins (mm2)
very low
conductance
board
low
conductance
board
high
conductance
board
Figure 5. SO-8 Thermal Resistance vs. PCB Configuration, Note 1, 2, 3
SL01250
0
50
100
150
0 100 200 300 400 500
Thermal resistance (C/W)
Cu area on fused pins (mm2)
very low
conductance
board
low
conductance
board
high
conductance
board
Figure 6. SO-14 Thermal Resistance vs. PCB Configuration, Note 1, 2, 3
