LM2575T-12 National Semiconductor, LM2575T-12 Datasheet - Page 11

• Manufacturer Part Number: LM2575T-12
• Description: Voltage Regulator IC
• Manufacturer: National Semiconductor

Specifications of LM2575T-12

• No. Of Pins: 5
• Output Current: 1A
• Peak Reflow Compatible (260 C): No
• Output Voltage: 12V
• Termination Type: Through Hole
• Supply Voltage Max: 40V
• Leaded Process Compatible: No
• Mounting Type: Through Hole
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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 pro-
cedure for the adjustable version.
B. From the inductor value selection guide, identify the induc-
tance region intersected by V
note the inductor 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 x I
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 recom-
mended.
Higher voltage electrolytic capacitors generally have lower
ESR numbers, and for this reasion it may be necessary to
select a capacitor rated for a higher voltage than would nor-
mally 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.
LM2575 Series Buck Regulator Design Procedure
LOAD
OUT
IN
(Max) = Maximum Input Voltage
(Max) = Maximum Load Current
PROCEDURE (Fixed Output Voltage Versions)
= Regulated Output Voltage (3.3V, 5V, 12V, or 15V)
LOAD
. For additional inductor information, see the
IN
)
IN
(Max) and I
OUT
)
LOAD
(Max), and
11
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
OUT
(Max) = 0.8A
= 5V
EXAMPLE (Fixed Output Voltage Versions)
= 100 µF to 470 µF standard aluminum electrolytic.
IN
)
OUT
)
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