AP1507-12D5A ETC, AP1507-12D5A Datasheet - Page 8

• Manufacturer Part Number: AP1507-12D5A
• Description: 150KHz/ 3A PWM Buck DC/DC Converter
• Manufacturer: ETC

150KHz, 3A PWM Buck DC/DC Converter
Pin Functions
+V
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 (+V
with a duty cycle of approximately V
minimize coupling to sensitive circuitry, the PC
board copper area connected to this pin should be
kept a minimum.
Feedback (FB)
Senses the regulated output voltage to complete
the feedback loop.
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 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
and ideally should have 2 or more square inches of
2 oz. Additional copper area improves the thermal
characteristics, but with copper areas greater than
approximately 6 in
heat dissipation are realized. If further thermal
improvements
multi-layer PC board with large copper areas and/or
airflow will be recommended.
Anachip Corp.
www.anachip.com.tw
ON /OFF (SD)
IN
Function Description
IN
– V
are
SAT
2
, only small improvements in
) and approximately – 0.5V,
needed,
double
OUT
/ V
IN
sided,
. To
2
,
8/9
The
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
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
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
temperature rise numbers are all approximate, and
there are many factors that will affect these
numbers.
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
Some of these factors include board
thermal
junction
regulator with
(TO-252
resistance
temperature
package)
all components
AP1507
Rev.1.1 Oct 29, 2004
and
for
junction
junction
various