LM2671N-5.0 National Semiconductor, LM2671N-5.0 Datasheet - Page 10

• Manufacturer Part Number: LM2671N-5.0
• Description: DC/DC Converter IC
• Manufacturer: National Semiconductor

Specifications of LM2671N-5.0

• Input Voltage: 40V
• Output Current: 500mA
• Output Voltage: 5V
• No. Of Pins: 8
• Mounting Type: Through Hole
• Voltage Regulator Type: Buck Switching
• Output Current Max: 0.5A
• Peak Reflow Compatible (260 C): No
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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C. Select an appropriate inductor from the four manufacturer’s
part numbers listed in Figure 8 . Each manufacturer makes a
different style of inductor to allow flexibility in meeting various
design requirements. Listed below are some of the
differentiating characteristics of each manufacturer’s inductors:
Schott: ferrite EP core inductors; these have very low leakage
magnetic fields to reduce electro-magnetic interference (EMI)
and are the lowest power loss inductors
Renco: ferrite stick core inductors; benefits are typically lowest
cost inductors and can withstand E • T and transient peak
currents above rated value. Be aware that these inductors
have an external magnetic field which may generate more EMI
than other types of inductors.
Pulse: powered iron toroid core inductors; these can also be
low cost and can withstand larger than normal E • T and
transient peak currents. Toroid inductors have low EMI.
Coilcraft: ferrite drum core inductors; these are the smallest
physical size inductors, available only as SMT components. Be
aware that these inductors also generate EMI — but less than
stick inductors.
Complete specifications for these inductors are available from
the respective manufacturers. A table listing the manufacturers’
phone numbers is located in Figure 9 .
2. Output Capacitor Selection (C
A. Select an output capacitor from the output capacitor table in
Figure 10 . Using the output voltage and the inductance value
found in the inductor selection guide, step 1, locate the
appropriate capacitor value and voltage rating.
The capacitor list contains through-hole electrolytic capacitors
from four different capacitor manufacturers and surface mount
tantalum capacitors from two different capacitor manufacturers.
It is recommended that both the manufacturers and the
manufacturer’s series that are listed in the table be used. A
table listing the manufacturers’ phone numbers is located in
Figure 11 .
3. Catch Diode Selection (D1)
A. In normal operation, the average current of the catch diode
is the load current times the catch diode duty cycle, 1-D (D is
the switch duty cycle, which is approximately the output
voltage divided by the input voltage). The largest value of the
catch diode average current occurs at the maximum load
current and maximum input voltage (minimum D). For normal
operation, the catch diode current rating must be at least 1.3
times greater than its maximum average current. However, if
the power supply design must withstand a continuous output
short, the diode should have a current rating equal to the
maximum current limit of the LM2671. The most stressful
condition for this diode is a shorted output condition.
B. The reverse voltage rating of the diode should be at least
1.25 times the maximum input voltage.
C. Because of their fast switching speed and low forward
voltage drop, Schottky diodes provide the best performance
and efficiency. This Schottky diode must be located close to
the LM2671 using short leads and short printed circuit traces.
LM2671 Series Buck Regulator Design Procedure (Fixed Output)
PROCEDURE (Fixed Output Voltage Version)
OUT
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10
C. The inductance value required is 47 µH. From the table in
Figure 8 , go to the L13 line and choose an inductor part
number from any of the four manufacturers shown. (In most
instances, both through hole and surface mount inductors are
available.)
2. Output Capacitor Selection (C
A. Use the 5.0V section in the output capacitor table in Figure
10 . Choose a capacitor value and voltage rating from the line
that contains the inductance value of 47 µH. The capacitance
and voltage rating values corresponding to the 47 µH inductor
are the:
Surface Mount:
68 µF/10V Sprague 594D Series.
100 µF/10V AVX TPS Series.
Through Hole:
68 µF/10V Sanyo OS-CON SA Series.
150 µF/35V Sanyo MV-GX Series.
150 µF/35V Nichicon PL Series.
150 µF/35V Panasonic HFQ Series.
3. Catch Diode Selection (D1)
A. Refer to the table shown in Figure 12 . In this example, a
1A, 20V Schottky diode will provide the best performance. If
the circuit must withstand a continuous shorted output, a
higher current Schottky diode is recommended.
EXAMPLE (Fixed Output Voltage Version)
OUT
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(Continued)