LM2671 datasheet(11/26 Pages) NSC

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LM2671 Series Buck Regulator Design Procedure (Fixed Output) (Continued)

PROCEDURE (Fixed Output Voltage Version)

EXAMPLE (Fixed Output Voltage Version)

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.

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. 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.

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.

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.

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