LM2675 Series Buck Regulator Design Procedure (Fixed Output) (Continued)
PROCEDURE (Fixed Output Voltage Version)
The capacitor list contains through-hole electrolytic capacitors
from four different capacitor manufacturers and surface mount
EXAMPLE (Fixed Output Voltage Version)
Surface Mount:
68 µF/10V Sprague 594D Series.
tantalum capacitors from two different capacitor manufacturers. 100 µF/10V AVX TPS Series.
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.
Through Hole:
68 µF/10V Sanyo OS-CON SA Series.
220 µF/35V Sanyo MV-GX Series.
220 µF/35V Nichicon PL Series.
220 µF/35V Panasonic HFQ Series.
3. Catch Diode Selection (D1)
3. Catch Diode Selection (D1)
A. In normal operation, the average current of the catch diode is A. Refer to the table shown in Figure 12. In this example, a 1A,
the load current times the catch diode duty cycle, 1-D (D is the 20V Schottky diode will provide the best performance. If 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 LM2675. The most stressful condition for this diode is a
shorted output condition.
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
LM2675 using short leads and short printed circuit traces.
4. Input Capacitor (CIN
)
4. Input Capacitor (CIN)
11
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