ap1509-s Diodes, Inc., ap1509-s Datasheet - Page 9

• Manufacturer Part Number: ap1509-s
• Description: 150khz, 2a Pwm Buck Dc/dc Converter
• Manufacturer: Diodes, Inc.

Function Description
Pin Functions
+V
This is the positive input supply for the IC switching regulator. A
suitable input bypass capacitor must be presented 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 (+V
V
approximately V
circuitry, the PC board copper area connected to this pin should
be minimized.
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.
AP1509 Rev. 2
SAT
IN
) and approximately – 0.5V, with a duty cycle of
OUT
/ V
IN
. To minimize coupling to sensitive
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IN
–
150KHz, 2A PWM BUCK DC/DC CONVERTER
Thermal Considerations
The SOP-8L 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
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 25
all approximate and are affected by many factors. Higher ambient
temperatures require more heat sinker.
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 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 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.
o
C (still air). These temperature increments are
©
FEBRUARY 2008
AP1509
Diodes Incorporated