AP1506

150KHz, 3A PWM BUCK DC/DC CONVERTER

AP1506

Document number: DS31015 Rev. 7 - 2

8 of 14

www.diodes.com

June 2010

© Diodes Incorporated

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.