Datasheet
2.5A 150KHZ PWM Buck DC/DC Converter
TD1507
October, 20, 2005.
Techcode Semiconductor Limited
9
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.
ON/OFF
Allows the switching regulator circuit to be
shutdown using logic level signals thus dropping
the total input supply current to approximately
80uA. 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
25V) shuts the regulator down. If this shutdown
feature is not needed, the ON /OFF 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 TD1507 is available in TO252-5L package.
The TO252 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 TD1507 junction temperature rises above
ambient temperature for a 2.5A load and different
input and output voltages.
The data for these
curves was taken with the TD1507 (TO252
package) operating as a buck switching regulator
in an ambient temperature of 25
oC (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.
The TO252 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
0.4 in
2, 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
2, only small
improvements in heat dissipation are realized. If
further thermal improvements are needed, double
sided, multilayer PC board with large copper
areas and/or airflow are recommended.
The
TD1507
(TO252
package)
junction
temperature rise above ambient temperature with
a 2.5A 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 2.5A are used,
double sided or multilayer 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.
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