LM2575S-3.3 National Semiconductor, LM2575S-3.3 Datasheet - Page 13

• Manufacturer Part Number: LM2575S-3.3
• Description: IC REG SIMPLE SWITCHER TO-263-5
• Manufacturer: National Semiconductor
• Series: SIMPLE SWITCHER®r
• Type: Step-Down (Buck)r

Specifications of LM2575S-3.3

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 3.3V
• Current - Output: 1A
• Frequency - Switching: 52kHz
• Voltage - Input: 4 ~ 40 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: D²Pak, TO-263 (5 leads + tab)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -
• Other names: *LM2575S-3.3

Given:
V
V
I
1. Inductor Selection (L1)
A. Select the correct Inductor value selection guide from Figures
3, 4, 5, 6 (Output voltages of 3.3V, 5V, 12V or 15V respectively).
For other output voltages, see the design procedure for the ad-
justable version.
B. From the inductor value selection guide, identify the inductance
region intersected by V
ductor code for that region.
C. Identify the inductor value from the inductor code, and select an
appropriate inductor from the table shown in Figure 9. Part numbers
are listed for three inductor manufacturers. The inductor chosen
must be rated for operation at the LM2575 switching frequency (52
kHz) and for a current rating of 1.15 × 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 de-
fines the dominate pole-pair of the switching regulator loop. For
stable operation and an acceptable output ripple voltage, (approx-
imately 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 ca-
pacitor 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 1.2 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 LM2575.
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.
LOAD
OUT
IN
LM2575 Series Buck Regulator Design Procedure
(Max) = Maximum Input Voltage
(Max) = Maximum Load Current
= Regulated Output Voltage (3.3V, 5V, 12V, or 15V)
PROCEDURE (Fixed Output Voltage Versions)
IN
)
IN
(Max) and I
OUT
LOAD
LOAD
)
(Max), and note the in-
. For additional inductor
13
Given:
V
V
I
1. Inductor Selection (L1)
A. Use the selection guide shown in Figure 4.
B. From the selection guide, the inductance area intersected by
the 20V line and 0.8A line is L330.
C. Inductor value required is 330 μH. From the table in Figure 9,
choose AIE 415-0926, Pulse Engineering PE-52627, or RL1952.
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 30V 1N5818 or SR103 Schottky diode, or any of the
suggested fast-recovery diodes shown in Figure 8.
4. Input Capacitor (C
A 47 μF, 25V aluminum electrolytic capacitor located near the input
and ground pins provides sufficient bypassing.
LOAD
OUT
IN
(Max) = 20V
(Max) = 0.8A
OUT
= 5V
= 100 μF to 470 μF standard aluminum electrolytic.
EXAMPLE (Fixed Output Voltage Versions)
IN
)
OUT
)
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