APA2068
Application Descriptions (Cont.)
Thermal Pad Considerations (Cont.)
internal dissipation figures are taken from the Power
Dissipation vs. Output Power graphs.
TAMax = TJMax -qJAPD
design issues are not properly addressed, the
APA2068 4W will go into thermal shutdown when
driving a 4W load.
(16)
150 - 45(0.8*2) = 78°C
The thermal padon thebottom of theAPA2068should
be soldered down to a copper padon thecircuit board.
Heat can be conducted away from the thermal pad
throughthecopperplanetoambient. If thecopperplane
is not on the top surface of the circuit board, 8 to 10
vias of 13 mil or smaller in diameter should be used to
thermally couple the thermal pad to the bottom plane.
The APA2068 is designed with a thermal shutdown
protection that turns the device off when the junction
temperaturesurpasses150°Ctopreventdamagingthe
IC.
For good thermal conduction, the vias must be plated
through and solder filled. The copper plane used to
conduct heat away from the thermal pad should be as
large as practical.
If the ambient temperatureishigher than25°C, a larger
copper plane or forced-air cooling will be required to
keep the APA2068 junction temperature below the
thermal shutdown temperature (150°C). In higher
ambient temperature, higher airflow rate and/or larger
copper area will be required to keep the IC out of
thermal shutdown.
Thermal Considerations
Linear power amplifiers dissipate a significant amount
of heat in the package under normal operating
conditions.
To calculate maximum ambient temperatures, first
consideration is that the numbers from the Power
Dissipation vs. Output Power graphs are per
channel values, sothe dissipation of theIC heat needs
tobedoubledfor two-channel operation.GivenqJA, the
maximum allowable junction temperature (TJMAX), and
the total internal dissipation (PD), the maximum
ambient temperature can be calculated with the
following equation. The maximum recommended
junction temperature for the APA2068 is 150°C. The
Copyright ã ANPEC Electronics Corp.
23
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Rev. A.2 - Jul., 2005
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