eorex

EP3101

Jul. 2006

www.eorex.com

10/13

Thermal Considerations

The EP3101 is available in two packages, a 5-pin TO-220 and a 5-pin surface mount TO-263. The

TO-220 package needs a heat sink under most conditions. The size of the heatsink depends on the input

voltage, the output voltage, the load current and the ambient temperature. The EP3101 junction

temperature rises above ambient temperature for a 3A load and different input and output voltages. The

data for these curves was taken with the EP3101 (TO-220 package) operating as a buck switching

regulator in an ambient temperature of 25°C (still air). These temperature rise numbers are all

approximate and there are many factors that can affect these temperatures. Higher ambient

temperatures require more heat sinking.

The TO-263 surface mount package tab is designed to be soldered to the copper on a printed circuit

board. The copper and the board are the heat sink for this package and the other heat producing

components, such as the catch diode and inductor. The PC board copper area that the package is

soldered to should be at least 0.4 in

copper area improves the thermal characteristics, but with copper areas greater than approximately 6 in

only small improvements in heat dissipation are realized. If further thermal improvements are needed,

double sided, multilayer PC board with large copper areas and/or airflow are recommended.

The EP3101 (TO-263 package) junction temperature rise 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 2A are used, double sided or multilayer 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, multilayer 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.