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TD1509 View Datasheet(PDF) - Unspecified

Part NameDescriptionManufacturer
TD1509 2A 150KHz PWM Buck DC/DC Converter Unspecified1
TD1509 Datasheet PDF : 17 Pages
First Prev 11 12 13 14 15 16 17
2A 150KHz PWM Buck DC/DC Converter
Function Description
Pin Functions
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
Circuit ground.
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.
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 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 TD1509 is available in two packages,.
The TD1509 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
TD1509 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.
The SOP8/DIP8 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 in2, 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 in2, 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 TD1509 junction temperature rise 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 2A 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
December, 20, 2005.
Techcode Semiconductor Limited
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