lm2593hvsx-adj National Semiconductor Corporation, lm2593hvsx-adj Datasheet - Page 18

• Manufacturer Part Number: lm2593hvsx-adj
• Description: Simple Switcher Power Converter 150 Khz 2a Step-down Voltage Regulator, With Features
• Manufacturer: National Semiconductor Corporation

www.national.com
Application Information
on the regulated positive output for the charge pump to work
correctly. Also, resistor R1 is required to limit the charging
current of C1 to some value less than the LM2593HV current
limit.
THERMAL CONSIDERATIONS
The LM2593HV is available in two packages, a 5-pin TO-220
(T) and a 5-pin surface mount TO-263 (S).
The TO-220 package needs a heat sink under most condi-
tions. The size of the heatsink depends on the input voltage,
the output voltage, the load current and the ambient tem-
perature. 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
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 6 in
small improvements in heat dissipation are realized. If fur-
ther thermal improvements are needed, double sided, mul-
tilayer PC board with large copper areas and/or airflow are
recommended.
The curves shown in Figure 15 show the LM2593HVS
(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
FIGURE 14. Charge Pump for Generating aLow Current, Negative Output Voltage
2
, and ideally should
(Continued)
2
, only
18
This method of generating a negative output voltage without
an additional inductor can be used with other members of
the Simple Switcher Family, using either the buck or boost
topology.
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, espe-
cially for high ambient temperatures and high output volt-
ages.
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.
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 surround-
ing air is still or moving. Furthermore, some of these com-
ponents 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.
10133348