ap1506-50t5r Diodes, Inc., ap1506-50t5r Datasheet - Page 9

• Manufacturer Part Number: ap1506-50t5r
• Description: 150khz, 3a Pwm Buck Dc/dc Converter
• Manufacturer: Diodes, Inc.

Functional 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 kept to 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 AP1506 is available in two packages: a 5-pin TO-220 and a
5-pin surface mount TO-263.
The TO-220 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
AP1506 junction temperature rises above ambient temperature
for a 3A load and different input and output voltages. The data for
these curves was taken with the AP1506 (TO-220 package)
operating as a buck-switching regulator in an ambient
temperature of 25
are all approximate and there are many factors that can affect
these temperatures. Higher ambient temperatures require more
heat sinking.
The TO-263 surface mount package tab was designed to be
soldering 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 in
inches of 2 oz. Additional copper area improves the thermal
characteristics, but with copper areas greater than approximately
6 in
further thermal improvements are needed, double sided,
multi-layer PC board with large copper areas and/or airflow will
be recommended.
AP1506 Rev. 5
SAT
IN
2
, only small improvements in heat dissipation are realized. If
) and approximately – 0.5V, with a duty cycle of
OUT
2
o
, and ideally should have 2 or more square
C (still air). These temperature rise numbers
/ V
IN
. To minimize coupling to sensitive
www.diodes.com
9 of 12
IN
150KHz, 3A PWM BUCK DC/DC CONVERTER
–
The AP1506 (TO-263 package) junction temperature rises 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 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 (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.
©
AP1506
Diodes Incorporated
MAY 2008