LM2595T-ADJ National Semiconductor, LM2595T-ADJ Datasheet - Page 10

• Manufacturer Part Number: LM2595T-ADJ
• Description: DC/DC Converter IC
• Manufacturer: National Semiconductor

Specifications of LM2595T-ADJ

• Input Voltage: 40V
• Output Current: 1A
• Output Voltage: 37V
• No. Of Pins: 5
• Termination Type: Through Hole
• Mounting Type: Through Hole
• Voltage Regulator Type: Buck Switching
• Output Current Max: 1A
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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LM2595 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 LM2595. 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 LM2595 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
1N5400 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 pin to prevent large volt-
age transients from appearing at the input. This capacitor
should be located close to the IC using short leads. In addi-
tion, the RMS current rating of the input capacitor should be
selected to be at least
manufacturers data sheet must be checked to assure that
this current rating is not exceeded. The curve shown in Fig-
ure 13 shows typical RMS current ratings for several different
aluminum electrolytic capacitor values.
For an aluminum electrolytic, the capacitor voltage rating
should be approximately 1.5 times the maximum input volt-
age. Caution must be exercised if solid tantalum capacitors
are used (see Application Information on input capacitor).
The tantalum capacitor voltage rating should be 2 times the
maximum input voltage and it is recommended 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)
IN
1
⁄
2
)
the DC load current. The capacitor
IN
pin.
10
3. Catch Diode Selection (D1)
A. Refer to the table shown in Figure 11 In this example, a
3A, 20V, 1N5820 Schottky diode will provide the best perfor-
mance, and will not be overstressed even for a shorted out-
put.
4. Input Capacitor (C
The important parameters for the Input capacitor are the in-
put voltage rating and the RMS current rating. With a nominal
input voltage of 12V, an aluminum electrolytic capacitor with
a voltage rating greater than 18V (1.5 x V
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 1A load, a capacitor with a RMS current
rating of at least 500 mA is needed. The curves shown in Fig-
ure 13 can be used to select an appropriate input capacitor.
From the curves, locate the 25V line and note which capaci-
tor values have RMS current ratings greater than 500 mA. Ei-
ther a 180 µF or 220 µF, 25V capacitor could be used.
For a through hole design, a 220 µF/25V 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 rat-
ings are adequate.
For surface mount designs, solid tantalum capacitors can be
used, but caution must be exercised with regard to the ca-
pacitor surge current rating (see Application Information on
input capacitors in this data sheet). The TPS series available
from AVX, and the 593D series from Sprague are both surge
current tested.
EXAMPLE (Fixed Output Voltage Version)
IN
)
1
⁄
2
the DC load current. In
(Continued)
IN
) would be