Datasheet

LM2598
www.ti.com SNVS125C –MARCH 1998–REVISED APRIL 2013
Circuit Data for Temperature Rise Curve DDPAK Package (S)
Capacitors Surface mount tantalum, molded “D” size
Inductor Surface mount, Schott, 68 μH
Diode Surface mount, 3A 40V, Schottky
PC board 3 square inches single sided 2 oz. copper (0.0028″)
Figure 40. Junction Temperature Rise, DDPAK
THERMAL CONSIDERATIONS
The LM2598 is available in two packages, a 7-pin TO-220 (T) and a 7-pin surface mount DDPAK (S).
The TO-220 package can be used without a heat sink for ambient temperatures up to approximately 50°C
(depending on the output voltage and load current). The curves in Figure 39 show the LM2598T junction
temperature rises above ambient temperature for different input and output voltages. The data for these curves
was taken with the LM2598T (TO-220 package) operating as a 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 some heat sinking, either to the PC board or a small
external heat sink.
The DDPAK 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
2
,
and ideally should have 2 or more square inches of 2 oz. (0.0028) in) copper. Additional copper area improves
the thermal characteristics, but with copper areas greater than approximately 3 in
2
, only small improvements in
heat dissipation are realized. If further thermal improvements are needed, double sided or multilayer PC-board
with large copper areas are recommended.
The curves shown in Figure 40 show the LM2598S (DDPAK package) junction temperature rise above ambient
temperature with a 1A 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.
For the best thermal performance, wide copper traces and generous amounts of printed circuit board copper
should be used in the board layout. (One 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.
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