Advanced Power
Electronics Corp. APE1702
FUNCTION DESCRIPTION
EN
THERMAL CONSIDERATIONS
6
Allows the switching regulator circuit to be shutdown using logic level signals thus
dropping the total input supple current to approximately 100uA. Pulling this pin below
a threshold voltage of approximately 1.3V turns the regulator on, and pulling this pin
above 1.3V (up to a maximum of VCC) shuts the regulator down. if this shutdown
feature is not needed, the EN pin can be wired to the ground pin.
The TO-263-5L package needs a heat sink under most conditions. The size of
the heat sink depends on the input voltage, the output voltage, the load current and
the ambient temperature. The APE1702 junction temperature rises above ambient
temperature for a 2A load and different input and output voltages.
The data for these curves was taken with the APE1702 (TO-263-5L package)
operating as a buck-switching regulator in an ambient temperature of 25°C (still air).
These temperature increments are all approximate and are affected by many factors.
Higher ambient temperatures required more heat sinker.
For the best thermal performance, wide copper traces and generous amounts of
printed circuit board copper (need connect to the VSS pins) should be used in the
board layout, (One exception is the SW pin, which should not have large areas of
copper.) to the surrounding air, and moving air lowers the thermal resistance even
further.
Package thermal resistance and junction temperature increments are all
approximate. The increments are affected by a lot of factors. 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.