lm2597hvn-5.0 National Semiconductor Corporation, lm2597hvn-5.0 Datasheet - Page 13

• Manufacturer Part Number: lm2597hvn-5.0
• Description: Simple Switcher Power Converter 150 Khz 0.5a Step-down Voltage Regulator, With Features
• Manufacturer: National Semiconductor Corporation

3. Output Capacitor Selection (C
A. In the majority of applications, low ESR electrolytic or solid
tantalum capacitors between 82 µF and 220 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 220 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 2 . This table contains
different 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 50 pF and 10 nF, and is wired in parallel with
the output voltage setting resistor, R
stability for high output voltages, low input-output voltages,
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 capacitors
made with Z5U material, they are not recommended.)
LM2597/LM2597HV Series Buck Regulator Design Procedure (Adjustable
Output)
PROCEDURE (Adjustable Output Voltage Version)
(Continued)
FF
) (See Figure 12 )
OUT
2
. It provides additional
)
13
3. Output Capacitor SeIection (C
A. See section on C
B. From the quick design table shown in Figure 2 , 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 capacitors
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 capacitor
would work. A 50V rating was chosen because it has a lower
ESR which provides a lower output ripple voltage.
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.
Refer to the capacitor manufacturers data sheet for this infor-
mation.
4. Feedforward Capacitor (C
The table shown in Figure 2 contains feed forward capacitor
values for various output voltages. In this example, a 1 nF
capacitor is needed.
120 µF 50V Nichicon PL Series
EXAMPLE (Adjustable Output Voltage Version)
82 µF 50V Panasonic HFQ Series
OUT
in Application Information section.
FF
)
OUT
)
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