LM2576, LM2576HV
SNVS107C –JUNE 1999–REVISED APRIL 2013
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LM2576 Series Buck Regulator Design Procedure
PROCEDURE (Fixed Output Voltage Versions)
EXAMPLE (Fixed Output Voltage Versions)
Given:
Given:
VOUT = 5V
VOUT = Regulated Output Voltage
(3.3V, 5V, 12V, or 15V)
VIN(Max) = 15V
ILOAD(Max) = 3A
VIN(Max) = Maximum Input Voltage
ILOAD(Max) = Maximum Load Current
1. Inductor Selection (L1)
1. Inductor Selection (L1)
A. Select the correct Inductor value selection guide from Figure 23, A. Use the selection guide shown in Figure 24.
Figure 24, Figure 25, or Figure 26. (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 selection guide, the inductance area intersected by the
15V line and 3A line is L100.
C. Inductor value required is 100 μH. From the table in Figure 23.
Choose AIE 415-0930, Pulse Engineering PE92108, or Renco
RL2444.
B. From the inductor value selection guide, identify the inductance
region intersected by VIN(Max) and ILOAD(Max), and 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 23. Part
numbers are listed for three inductor manufacturers. The inductor
chosen must be rated for operation at the LM2576 switching
frequency (52 kHz) and for a current rating of 1.15 × ILOAD. For
additional inductor information, see INDUCTOR SELECTION.
2. Output Capacitor Selection (COUT
)
2. Output Capacitor Selection (COUT)
A. The value of the output capacitor together with the inductor A. COUT = 680 μF to 2000 μF standard aluminum electrolytic.
defines the dominate pole-pair of the switching regulator loop. For
B.Capacitor voltage rating = 20V.
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)
3. Catch Diode Selection (D1)
A.The catch-diode current rating must be at least 1.2 times greater A.For this example, a 3A current rating is adequate.
than the maximum load current. Also, if the power supply design
B. Use a 20V 1N5823 or SR302 Schottky diode, or any of the
must withstand a continuous output short, the diode should have a
suggested fast-recovery diodes shown in Table 1.
current rating equal to the maximum current limit of the LM2576. 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 (CIN
An aluminum or tantalum electrolytic bypass capacitor located close A 100 μF, 25V aluminum electrolytic capacitor located near the input
to the regulator is needed for stable operation. and ground pins provides sufficient bypassing.
)
4. Input Capacitor (CIN)
12
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