LM2574M-12 National Semiconductor, LM2574M-12 Datasheet - Page 14

• Manufacturer Part Number: LM2574M-12
• Description: IC,SMPS CONTROLLER,VOLTAGE-MODE,BIPOLAR,SOP,14PIN,PLASTIC
• Manufacturer: National Semiconductor

Specifications of LM2574M-12

• Rohs Compliant: NO

Given: V
15V) V
Maximum Load Current
1. Inductor Selection (L1)
A. Select the correct Inductor value selection guide from
Figures 4, 5, 6, or Figure 7. (Output voltages of 3.3V, 5V,
12V or 15V respectively). For other output voltages, see the
design procedure for the adjustable version.
B. From the inductor value selection guide, identify the
inductance region intersected by V
C. Select an appropriate inductor from the table shown in
Figure 3. Part numbers are listed for three inductor
manufacturers. The inductor chosen must be rated for
operation at the LM2574 switching frequency (52 kHz) and
for a current rating of 1.5 x I
information, see the inductor section in the Application Hints
section of this data sheet.
2. Output Capacitor Selection (C
A. The value of the output capacitor together with the
inductor defines the dominate pole-pair of the switching
regulator loop. For stable operation and an acceptable output
ripple voltage, (approximately 1% of the output voltage) a
value between 100 µF and 470 µF is recommended.
B. The capacitor’s voltage rating should be at least 1.5 times
greater than the output voltage. For a 5V regulator, a rating
of at least 8V is appropriate, and a 10V or 15V rating is
recommended.
Higher voltage electrolytic capacitors generally have lower
ESR numbers, and for this reason it may be necessary to
select a capacitor rated for a higher voltage than would
normally be needed.
3. Catch Diode Selection (D1)
A. The catch-diode current rating must be at least 1.5 times
greater than the maximum load current. Also, 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 LM2574. The most stressful condition for
this diode is an overload or shorted output condition.
B. The reverse voltage rating of the diode should be at least
1.25 times the maximum input voltage.
4. Input Capacitor (C
An aluminum or tantalum electrolytic bypass capacitor
located close to the regulator is needed for stable operation.
LM2574 Series Buck Regulator
Design Procedure
PROCEDURE (Fixed Output Voltage Versions)
IN
(Max) = Maximum Input Voltage I
OUT
= Regulated Output Voltage (3.3V, 5V, 12V, or
IN
)
LOAD
. For additional inductor
IN
OUT
(Max) and I
)
LOAD
(Max) =
LOAD
(Max).
13
Given: V
1. Inductor Selection (L1)
A. Use the selection guide shown in Figure 5.
B. From the selection guide, the inductance area intersected
by the 15V line and 0.4A line is 330.
C. Inductor value required is 330 µH. From the table in
Figure 3, choose Pulse Engineering PE-52627, Renco
RL-1284-330, or NPI NP5920/5921.
2. Output Capacitor Selection (C
A. C
B. Capacitor voltage rating = 20V.
3. Catch Diode Selection (D1)
A. For this example, a 1A current rating is adequate.
B. Use a 20V 1N5817 or SR102 Schottky diode, or any of
the suggested fast-recovery diodes shown in Figure 9.
4. Input Capacitor (C
A 22 µF aluminum electrolytic capacitor located near the
input and ground pins provides sufficient bypassing.
OUT
EXAMPLE (Fixed Output Voltage Versions)
= 100 µF to 470 µF standard aluminum electrolytic.
OUT
= 5V V
IN
IN
(Max) = 15V I
)
OUT
LOAD
)
(Max) = 0.4A
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