LM2574M-12 National Semiconductor, LM2574M-12 Datasheet - Page 17

• 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

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3. 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, the capacitor must
satisfy the following requirement:
1000 µF that will satisfy the loop requirements for stable op-
eration. But to achieve an acceptable output ripple voltage,
(approximately 1% of the output voltage) and transient re-
sponse, the output capacitor may need to be several times
larger than the above formula yields.
B. The capacitor’s voltage rating should be at last 1.5 times
greater than the output voltage. For a 24V regulator, a rating of
at least 35V is recommended. Higher voltage electrolytic ca-
pacitors generally have lower ESR numbers, and for this rea-
sion it may be necessary to select a capacitor rate for a higher
voltage than would normally be needed.
4. 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. Suitable
diodes are shown in the selection guide of Figure 9.
B. The reverse voltage rating of the diode should be at least
1.25 times the maximum input voltage.
5. Input Capacitor (C
electrolytic bypass capacitor located close to the regulator is
needed for stable operation.
LM2574 Series Buck Regulator Design Procedure
The above formula yields capacitor values between 5 µF and
PROCEDURE (Adjustable Output Voltage Versions)
IN
) An aluminum or tantalum
OUT
)
16
3. Output Capacitor Selection (C
100 µF C
4. Catch Diode Selection (D1)
A. For this example, a 1A current rating is adequate.
B. Use a 50V MBR150 or 11DQ05 Schottky diode, or any of
the suggested fast-recovery diodes in Figure 9.
5. Input Capacitor (C
A 22 µF aluminum electrolytic capacitor located near the
input and ground pins provides sufficient bypassing. See
(Figure 9).
To further simplify the buck regulator design procedure,
National Semiconductor is making available computer design
software to be used with the Simple Switcher line of
switching regulators. Switchers Made Simple (version 3.3) is
available on a (3
from a National Semiconductor sales office in your area.
However, for acceptable output ripple voltage select C
EXAMPLE (Adjustable Output Voltage Versions)
OUT
= 100 µF electrolytic capacitor
1
⁄
2
") diskette for IBM compatible computers
(Continued)
IN
)
OUT
)
OUT
≥