LM2599SX-12/NOPB National Semiconductor, LM2599SX-12/NOPB Datasheet - Page 14

• Manufacturer Part Number: LM2599SX-12/NOPB
• Description: IC REG SW 12V 3A STP DN TO-263-7
• Manufacturer: National Semiconductor
• Series: SIMPLE SWITCHER®r
• Type: Step-Down (Buck)r

Specifications of LM2599SX-12/NOPB

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 12V
• Current - Output: 3A
• Frequency - Switching: 150kHz
• Voltage - Input: 4.5 ~ 40 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: D²Pak, TO-263 (7 leads + tab)
• For Use With: 551011367-021 - BOARD WEBENCH BUILD IT LM2599
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Other names: *LM2599SX-12; *LM2599SX-12/NOPB; LM2599SX-12

www.national.com
LM2599 Series Buck Regulator Design Procedure (Adjustable Output)
5. Catch Diode Selection (D1)
A. The catch diode current rating must be at least 1.3 times
greater than the maximum load current. Also, if the power
supply design must withstand a continuous output short, the
diode should have a current rating equal to the maximum
current limit of the LM2599. 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 LM2599 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 are also a
good choice, but some types with an abrupt turn-off charac-
teristic may cause instability or EMl problems. Ultra-fast re-
covery diodes typically have reverse recovery times of 50 ns
or less. Rectifiers such as the 1N4001 series are much too
slow and should not be used.
6. Input Capacitor (C
A low ESR aluminum or tantalum bypass capacitor is needed
between the input pin and ground to prevent large voltage
transients from appearing at the input. In addition, the RMS
current rating of the input capacitor should be selected to be
at least
data sheet must be checked to assure that this current rating
is not exceeded. The curve shown in Figure 16 shows typical
RMS current ratings for several different aluminum electro-
lytic capacitor values.
This capacitor should be located close to the IC using short
leads and the voltage rating should be approximately 1.5
times the maximum input voltage.
If solid tantalum input capacitors are used, it is recomended
that they be surge current tested by the manufacturer.
Use caution when using a high dielectric constant ceramic
capacitor for input bypassing, because it may cause severe
ringing at the V
For additional information, see section on input capaci-
tor in application information section.
(Continued)
PROCEDURE (Adjustable Output Voltage Version)
1
⁄
2
the DC load current. The capacitor manufacturers
IN
pin.
IN
)
14
5. Catch Diode Selection (D1)
A. Refer to the table shown in Figure 11 . Schottky diodes
later) is available on a 3
provide the best performance, and in this example a 3A, 40V,
1N5825 Schottky diode would be a good choice. The 3A
diode rating is more than adequate and will not be over-
stressed even for a shorted output.
6. Input Capacitor (C
The important parameters for the Input capacitor are the
input voltage rating and the RMS current rating. With a
nominal input voltage of 28V, an aluminum electrolytic alumi-
num electrolytic capacitor with a voltage rating greater than
42V (1.5 x V
capacitor voltage rating is 50V, a 50V capacitor should be
used. The capacitor voltage rating of (1.5 x V
vative guideline, and can be modified somewhat if desired.
The RMS current rating requirement for the input capacitor of
a buck regulator is approximately
this example, with a 3A load, a capacitor with a RMS current
rating of at least 1.5A is needed.
The curves shown in Figure 16 can be used to select an
appropriate input capacitor. From the curves, locate the 50V
line and note which capacitor values have RMS current
ratings greater than 1.5A. Either a 470 µF or 680 µF, 50V
capacitor could be used.
For a through hole design, a 680 µF/50V electrolytic capaci-
tor (Panasonic HFQ series or Nichicon PL series or equiva-
lent) would be adequate. Other types or other manufacturers
capacitors can be used provided the RMS ripple current
ratings are adequate.
For surface mount designs, solid tantalum capacitors can be
used, but caution must be exercised with regard to the
capacitor sure current rating (see Application Information or
input capacitors in this data sheet). The TPS series available
from AVX, and the 593D series from Sprague are both surge
current tested.
To further simplify the buck regulator design procedure, Na-
tional Semiconductor is making available computer design
software to be used with the Simple Switcher line ot switch-
ing regulators. Switchers Made Simple (version 4.2.1 or
computers.
EXAMPLE (Adjustable Output Voltage Version)
IN
) would be needed. Since the the next higher
IN
)
1
⁄
2
" diskette for IBM compatible
1
⁄
2
the DC load current. In
IN
) is a conser-