LM2596S-12 National Semiconductor, LM2596S-12 Datasheet - Page 13

• Manufacturer Part Number: LM2596S-12
• Description: DC/DC Converter IC
• Manufacturer: National Semiconductor

Specifications of LM2596S-12

• Input Voltage: 40V
• Output Current: 3A
• Output Voltage: 12V
• No. Of Pins: 5
• Termination Type: SMD
• Mounting Type: Through Hole
• Voltage Regulator Type: Buck Switching
• Output Current Max: 3A
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

LM2596 Series Buck Regulator Design Procedure (Adjustable Output)
3. Output Capacitor Selection (C
A. In the majority of applications, low ESR electrolytic or solid
tantalum capacitors between 82 µF and 820 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. For additional informa-
tion, see section on output capacitors in application in-
formation section.
B. To simplify the capacitor selection procedure, refer to the
quick design table shown in Figure 3 . This table contains dif-
ferent output voltages, and lists various output capacitors
that will provide the best design solutions.
C. The capacitor voltage rating should be at least 1.5 times
greater than the output voltage, and often much higher volt-
age ratings are needed to satisfy the low ESR requirements
needed for low output ripple voltage.
4. Feedforward Capacitor (C
For output voltages greater than approximately 10V, an addi-
tional capacitor is required. The compensation capacitor is
typically between 100 pF and 33 nF, and is wired in parallel
with the output voltage setting resistor, R
tional stability for high output voltages, low input-output volt-
ages, and/or very low ESR output capacitors, such as solid
tantalum capacitors.
This capacitor type can be ceramic, plastic, silver mica, etc.
(Because of the unstable characteristics of ceramic capaci-
tors made with Z5U material, they are not recommended.)
(Continued)
PROCEDURE (Adjustable Output Voltage Version)
FF
) (See Figure 1 )
OUT
)
2
. It provides addi-
13
3. Output Capacitor SeIection (C
A. See section on C
B. From the quick design table shown in Figure 3 , locate the
output voltage column. From that column, locate the output
voltage closest to the output voltage in your application. In
this example, select the 24V line. Under the output capacitor
section, select a capacitor from the list of through hole elec-
trolytic or surface mount tantalum types from four different
capacitor manufacturers. It is recommended that both the
manufacturers and the manufacturers series that are listed in
the table be used.
In this example, through hole aluminum electrolytic capaci-
tors from several different manufacturers are available.
C. For a 20V output, a capacitor rating of at least 30V or
more is needed. In this example, either a 35V or 50V capaci-
tor would work. A 35V rating was chosen, although a 50V rat-
ing could also be used if a lower output ripple voltage is
needed.
Other manufacturers or other types of capacitors may also
be used, provided the capacitor specifications (especially the
100 kHz ESR) closely match the types listed in the table. Re-
fer to the capacitor manufacturers data sheet for this informa-
tion.
4. Feedforward Capacitor (C
The table shown in Figure 3 contains feed forward capacitor
values for various output voltages. In this example, a 560 pF
capacitor is needed.
220 µF/35V Panasonic HFQ Series
150 µF/35V Nichicon PL Series
EXAMPLE (Adjustable Output Voltage Version)
OUT
in Application Information section.
FF
)
OUT
)
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