AP1509-33S Просмотр технического описания (PDF) - Anachip Corporation
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AP1509-33S Datasheet PDF : 8 Pages
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150KHz, 2A PWM Buck DC/DC Converter
AP1509
Function Description
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 a minimum.
Feedback
Senses the regulated output voltage to complete
the feedback loop.
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 SD pin can be wired to
the ground pin or it can be left open, in either case
the regulator will be in the ON condition.
Thermal Considerations
The SOP-8 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 AP1509 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
AP1509 (SOP-8 package) operating as a
buck-switching regulator in an ambient temperature
of 25oC (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.
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, 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.
Anachip Corp.
www.anachip.com.tw
Rev.0.1 Nov 27, 2003
7/8
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