AP1507(2007) 데이터 시트보기 (PDF) - Diodes Incorporated.
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AP1507 Datasheet PDF : 10 Pages
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AP1507
150KHz, 3A PWM BUCK DC/DC CONVERTER
Applications Information
Pin Functions
+VIN
This is the positive input supply for the IC switching regulator. A
suitable input bypass capacitor must be present at this pin to
minimize voltage transients and to supply the switching currents
needed by the regulator.
Ground
Circuit ground.
Output
Internal switch. The voltage at this pin switches between (+VIN –
VSAT) and approximately – 0.5V, with a duty cycle of
approximately VOUT / VIN. To minimize coupling to sensitive
circuitry, the PC board copper area connected to this pin should
be kept at a minimum.
Feedback (FB)
Senses the regulated output voltage to complete the feedback
loop.
ON /OFF (SD)
Allows the switching regulator circuit to be shutdown using logic
level signals thus dropping the total input supply current to
approximately 150uA. 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 18V) shuts the regulator down.
If this shutdown feature is not needed, the ON /OFF pin can be
wired to the ground pin.
Thermal Considerations
The TO-252 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 0.8 in2, and ideally should have 2 or more
square inches of 2 oz. additional copper area which improves the
thermal characteristics. With copper areas greater than
approximately 6 in2, only small improvements in heat dissipation
are realized. If further thermal improvements are needed, double
sided, multi-layer PC board with large copper areas and/or airflow
will be recommended.
The AP1507 (TO-252 package) junction temperature rises above
ambient temperature with a 3A 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
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. (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, 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.
AP1507 Rev. 1
8 of 10
www.diodes.com
FEBRUARY 2007
© Diodes Incorporated
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