lm2595sx-adj National Semiconductor Corporation, lm2595sx-adj Datasheet - Page 9

• Manufacturer Part Number: lm2595sx-adj
• Description: Simple Switcher Power Converter 150 Khz 1a Step-down Voltage Regulator
• Manufacturer: National Semiconductor Corporation

LM2595 Series Buck Regulator Design Procedure (Fixed Output)
Given:
V
V
I
1. Inductor Selection (L1)
A. Select the correct inductor value selection guide from Fig-
ure 4 , Figure 5 , or Figure 6 . (Output voltages of 3.3V, 5V, or
12V respectively.) For all other voltages, see the design pro-
cedure for the adjustable version.
B. From the inductor value selection guide, identify the induc-
tance region intersected by the Maximum Input Voltage line
and the Maximum Load Current line. Each region is identified
by an inductance value and an inductor code (LXX).
C. Select an appropriate inductor from the four manufactur-
er’s part numbers listed in Figure 8 .
2. Output Capacitor Selection (C
A. In the majority of applications, low ESR (Equivalent Series
Resistance) electrolytic capacitors between 47 µF and 330
µF and low ESR solid tantalum capacitors between 56 µF
and 270 µF provide the best results. This capacitor should be
located close to the IC using short capacitor leads and short
copper traces. Do not use capacitors larger than 330 µF.
For additional information, see section on output capaci-
tors in application information section.
B. To simplify the capacitor selection procedure, refer to the
quick design component selection table shown in Figure 2 .
This table contains different input voltages, output voltages,
and load currents, and lists various inductors and output ca-
pacitors that will provide the best design solutions.
C. The capacitor voltage rating for electrolytic capacitors
should be at least 1.5 times greater than the output voltage,
and often much higher voltage ratings are needed to satisfy
the low ESR requirements for low output ripple voltage.
D. For computer aided design software, see Switchers
Made Simple
Procedure continued on next page.
LOAD
OUT
IN
(max) = Maximum DC Input Voltage
(max) = Maximum Load Current
PROCEDURE (Fixed Output Voltage Version)
= Regulated Output Voltage (3.3V, 5V or 12V)
®
version 4.2 or later.
OUT
)
9
Given:
V
V
I
1. Inductor Selection (L1)
A. Use the inductor selection guide for the 5V version shown
in Figure 5 .
B. From the inductor value selection guide shown in Figure 5 ,
the inductance region intersected by the 12V horizontal line
and the 1A vertical line is 68 µH, and the inductor code is
L30.
C. The inductance value required is 68 µH. From the table in
Figure 8 , go to the L30 line and choose an inductor part num-
ber from any of the four manufacturers shown. (In most in-
stance, both through hole and surface mount inductors are
available.)
2. Output Capacitor Selection (C
A. See section on output capacitors in application infor-
mation section.
B. From the quick design component selection table shown
in Figure 2 , locate the 5V output voltage section. In the load
current column, choose the load current line that is closest to
the current needed in your application, for this example, use
the 1A line. In the maximum input voltage column, select the
line that covers the input 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.
The capacitor list contains both through hole electrolytic and
surface mount tantalum capacitors from four different capaci-
tor manufacturers. It is recommended that both the manufac-
turers and the manufacturer’s series that are listed in the
table be used.
In this example aluminum electrolytic capacitors from several
different manufacturers are available with the range of ESR
numbers needed.
C. For a 5V output, a capacitor voltage rating at least 7.5V or
more is needed. But, in this example, even a low ESR,
switching grade, 220 µF 10V aluminum electrolytic capacitor
would exhibit approximately 225 m
in Figure 14 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 ca-
pacitor with a higher voltage rating (lower ESR) should be se-
lected. A 16V or 25V capacitor will reduce the ripple voltage
by approximately half.
Example continued on next page.
LOAD
OUT
IN
(max) = 12V
220 µF 25V Panasonic HFQ Series
220 µF 25V Nichicon PL Series
(max) = 1A
= 5V
EXAMPLE (Fixed Output Voltage Version)
OUT
of ESR (see the curve
)
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