LM2599SX-12/NOPB National Semiconductor, LM2599SX-12/NOPB Datasheet - Page 11

• 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

LM2599 Series Buck Regulator Design Procedure (Fixed Output)
3. 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 also provide
good results. Ultra-fast recovery diodes typically have re-
verse recovery times of 50 ns or less. Rectifiers such as the
IN5400 series are much too slow and should not be used.
4. 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 ceramic capacitors for input bypass-
ing, because it may cause severe ringing at the V
For additional information, see section on input capaci-
tors in Application Information section.
PROCEDURE (Fixed Output Voltage Version)
1
⁄
2
the DC load current. The capacitor manufacturers
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IN
pin.
11
3. Catch Diode Selection (D1)
A. Refer to the table shown in Figure 11 . In this example, a
5A, 20V, 1N5823 Schottky diode will provide the best perfor-
mance, and will not be overstressed even for a shorted
output.
4. 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 12V, an aluminum electrolytic ca-
pacitor with a voltage rating greater than 18V (1.5 x V
would be needed. The next higher capacitor voltage rating is
25V.
The RMS current rating requirement for the input capacitor in
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 35V line and note which capaci-
tor values have RMS current ratings greater than 1.5A. A
680 µF, 35V capacitor could be used.
For a through hole design, a 680 µF/35V 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 are
recommended. The TPS series available from AVX, and the
593D series from Sprague are both surge current tested.
EXAMPLE (Fixed Output Voltage Version)
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1
⁄
2
the DC load current. In
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