LM2596 Просмотр технического описания (PDF) - Estek Electronics Co. Ltd
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LM2596 Datasheet PDF : 13 Pages
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LM2596
LM2596 SERIES BUCK REGULATOR DESIGN PROCEDURE (FIXED OUTPUT)
PROCEDURE (Fixed Output Voltage Version)
Given:
Given:
VOUT = Regulated Output Voltage (3.3V, 5V or 12V)
VIN (max) = Maximum DC Input Voltage
I (max) = Maximum Load Current
1. Inductor Selection (L1)
A. Select the correct inductor value selection guide from Figures
Figure 4, Figure 5,or Figure 6. (Output voltages of 3.3V, 5V, or
12V respectively.) For all other voltages, see the design procedure
for the adjustable version.
B. From the inductor value selection guide, identify the inductance
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 manufacturer’s part
numbers listed in Figure 8.
EXAMPLE (Fixed Output Voltage Version)
VOUT =5V
VIN (max) = 12V
I (max) = 3A
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 3A
vertical line is 33 µH, and the inductor code is L40.
C. The inductance value required is 33 µH. From the table in Figure 8, go to the
L40 line and choose an inductor part number from any of the four manufacturers
shown. (In most in-stance, both through hole and surface mount inductors are
available.)
2. Output Capacitor Selection (COUT)
A. In the majority of applications, low ESR (Equivalent Series
Resistance) electrolytic capacitors between 82 µF and 820 µF and
low ESR solid tantalum capacitors between 10 µF and 470 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 820 µF.
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 capacitors that will
provide the best design solutions.
2. Output Capacitor Selection (COUT)
A. See section on output capacitors in application information 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 3A
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 capacitor manufacturers. It is recommended that both
the manufacturers 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.
330 µF 35V Panasonic HFQ Series
330 µF 35V Nichicon PL Series
C. The capacitor voltage rating for electrolytic capacitors should be C. For a 5V output, a capacitor voltage rating at least 7.5V or more is needed. But
at least 1.5 times greater than the output voltage, and often much even a low ESR, switching grade, 220µF 10V aluminum electrolytic capacitor
higher voltage ratings are needed to satisfy the low ESR
would exhibit approximately 225 mW of ESR (see the curve in Figure 14 for the
requirements for low output ripple voltage.
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 volt-age by approximately half.
3. Catch Diode Selection (D1)
3. Catch Diode Selection (D1)
A. The catch diode current rating must be at least 1.3 times greater than the A. Refer to the table shown in Figure 11. In this example, a 5A, 20V, 1N5823
maximum load current. Also, if the power supply design must withstand a Schottky diode will provide the best performance, and will not be overstressed even
continuous output short, the diode should have a current rating equal to the for a shorted output.
maximum current limit of the LM2596. 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.
C. This diode must be fast (short reverse recovery time) and must be located
close to the LM2596 using short leads and short printed circuit traces.
Because of their fast switching speed and low forward voltage drop,
Schottky diodes provide the best performance and efficiency, and should be
the first choice, especially in low output voltage applications.
Ultra-fast recovery, or High-Efficiency rectifiers also provide good results.
Ultra-fast recovery diodes typically have reverse recovery times of 50 ns or
less. Rectifiers such as the 1N5400 series are much too slow and should not
be used.
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