Ap1506 – Diodes AP1506 User Manual
Page 8
AP1506
150KHz, 3A PWM BUCK DC/DC CONVERTER
AP1506
Document number: DS31015 Rev. 7 - 2
8 of 14
June 2010
© Diodes Incorporated
Functional Description
(Continued)
The AP1506 (TO263 package) junction temperature rises above ambient temperature with a 2A load for various
input and output voltages. This data was taken with the circuit operating as a buck-switching regulator with all
components mounted on a PC board to simulate the junction temperature under actual operating conditions. This
curve can be used for a quick check for the approximate junction temperature for various conditions, but be aware
that there are many factors that can affect the junction temperature. When load currents higher than 3A are used,
double sided or multi-layer PC boards with large copper areas and/or airflow might be needed, especially for high
ambient temperatures and high output voltages.
For the best thermal performance, wide copper traces and generous amounts of printed circuit board copper
should be used in the board layout (Once exception to this is the output (switch) pin, which should not have large
areas of copper). Large areas of copper provide the best transfer of heat (lower thermal resistance) to the
surrounding air, and moving air lowers the thermal resistance even further.
Package thermal resistance and junction temperature rise numbers are all approximate, and there are many
factors that will affect these numbers. Some of these factors include board size, shape, thickness, position,
location, and even board temperature. Other factors are: trace width, total printed circuit copper area, copper
thickness, single or double-sided, multi-layer board and the amount of solder on the board. The effectiveness of
the PC board to dissipate heat also depends on the size, quantity and spacing of other components on the board,
as well as whether the surrounding air is still or moving. Furthermore, some of these components such as the
catch diode will add heat to the PC board and the heat can vary as the input voltage changes. For the inductor,
depending on the physical size, type of core material and the DC resistance, it could either act as a heat sink
taking heat away from the board, or it could add heat to the board.