TD1583 Techcode, TD1583 Datasheet - Page 9

• Manufacturer Part Number: TD1583
• Description: 3A 380Khz 28V PWM Buck DC/DC Converter
• Manufacturer: Techcode

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Function Description
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
Gnd
Circuit ground.
SW
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.
FB
Senses the regulated output voltage to complete
the feedback loop.
EN
Allows the switching regulator circuit to be
shutdown using logic level signals thus dropping
the total input supply current to approximately
30uA. Pulling this pin below a threshold voltage of
approximately 1.3V turns the regulator down, and
pulling this pin above 1.3V (up to a maximum of
12V) shuts the regulator on. Forautomatic starup
condition , can be implemented by the addition of
a resistive voltage divider from V
Thermal Considerations
The TD1583 is available in SOP8 package.
The SOP8 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
TD1583
ambient temperature for a 3A load and different
input and output voltages. The data for these
curves was taken with the TD1583 (SOP8
package) operating as a buck-switching regulator
in an ambient temperature of 25
These
approximate and there are many factors that can
IN
September, 2006
3A 380KHZ 28V PWM Buck DC/DC Converter
temperature
junction
IN
– V
SAT
) and approximately – 0.5V,
temperature
rise
numbers
IN
to GND.
rises
o
OUT
C (still air).
/ V
are
above
IN
. To
all
9
affect
temperatures require more heat sinking.
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. 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.
Setting the Output Voltage
The output voltage is set using a resistive
voltage divider from the output voltage to FB. The
voltage divider divides the
output voltage down by the ratio:
VFB = VOUT * R2 / (R1 + R2)
Thus the output voltage is:
VOUT = 1.222 * (R1 + R2) / R2
R2 can be as high as 100KΩ, but a typical
value is 10KΩ. Using that value, R1 is
determined by:
R1 ~= 8.18 * (VOUT – 1.222) (KΩ)
For example, for a 3.3V output voltage, R2 is
10KΩ, and R1 is 17KΩ.
these
thermal
temperatures.
Techcode Semiconductor Limited
resistance
Higher
TD1583
Datasheet
and
ambient
junction