LM2596
SNVS124C –NOVEMBER 1999–REVISED APRIL 2013
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LM2596 Series Buck Regulator Design Procedure (Fixed Output)
PROCEDURE (Fixed Output Voltage Version)
EXAMPLE (Fixed Output Voltage Version)
Given:
Given:
VOUT = Regulated Output Voltage (3.3V, 5V or 12V)
VIN(max) = Maximum DC Input Voltage
ILOAD(max) = Maximum Load Current
VOUT = 5V
VIN(max) = 12V
ILOAD(max) = 3A
1. Inductor Selection (L1)
1. Inductor Selection (L1)
A. Select the correct inductor value selection guide from Figures A. Use the inductor selection guide for the 5V version shown in
Figure 21, Figure 22, or Figure 23. (Output voltages of 3.3V, 5V, or Figure 22.
12V respectively.) For all other voltages, see the Design Procedure
for the adjustable version.
B. From the inductor value selection guide shown in Figure 22, the
inductance region intersected by the 12V horizontal line and the 3A
B. From the inductor value selection guide, identify the inductance vertical line is 33 μH, and the inductor code is L40.
region intersected by the Maximum Input Voltage line and the
C. The inductance value required is 33 μH. From the table in
Maximum Load Current line. Each region is identified by an
Table 3, go to the L40 line and choose an inductor part number from
inductance value and an inductor code (LXX).
any of the four manufacturers shown. (In most instance, both
C. Select an appropriate inductor from the four manufacturer's part through hole and surface mount inductors are available.)
numbers listed in Table 3.
2. Output Capacitor Selection (COUT
)
2. Output Capacitor Selection (COUT)
A. In the majority of applications, low ESR (Equivalent Series A. See section on output capacitors in Application Information
Resistance) electrolytic capacitors between 82 μF and 820 μF and section.
low ESR solid tantalum capacitors between 10 μF and 470 μF
B. From the quick design component selection table shown in
provide the best results. This capacitor should be located close to
Table 1, locate the 5V output voltage section. In the load current
the IC using short capacitor leads and short copper traces. Do not
column, choose the load current line that is closest to the current
use capacitors larger than 820 μF .
needed in your application, for this example, use the 3A line. In the
For additional information, see section on output capacitors in maximum input voltage column, select the line that covers the input
Application Information section.
voltage needed in your application, in this example, use the 15V line.
Continuing on this line are recommended inductors and capacitors
that will provide the best overall performance.
B. To simplify the capacitor selection procedure, refer to the quick
design component selection table shown in Table 1. This table
contains different input voltages, output voltages, and load currents, The capacitor list contains both through hole electrolytic and surface
and lists various inductors and output capacitors that will provide the mount tantalum capacitors from four different capacitor
best design solutions.
manufacturers. It is recommended that both the manufacturers and
the manufacturer's series that are listed in the table be used.
C. The capacitor voltage rating for electrolytic capacitors should be
at least 1.5 times greater than the output voltage, and often much In this example aluminum electrolytic capacitors from several
higher voltage ratings are needed to satisfy the low ESR different manufacturers are available with the range of ESR numbers
requirements for low output ripple voltage.
needed.
D. For computer aided design software, see Switchers Made
330 μF 35V Panasonic HFQ Series
Simple™ version 4.3 or later.
330 μF 35V Nichicon PL Series
C. For a 5V output, a capacitor voltage rating at least 7.5V or more
is needed. But even a low ESR, switching grade, 220 μF 10V
aluminum electrolytic capacitor would exhibit approximately 225 mΩ
of ESR (see the curve in Figure 26 for the ESR vs voltage rating).
This amount of ESR would result in relatively high output ripple
voltage. To reduce the ripple to 1% of the output voltage, or less, a
capacitor with a higher value or with a higher voltage rating (lower
ESR) should be selected. A 16V or 25V capacitor will reduce the
ripple voltage by approximately half.
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