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| 型号： | 5962-9650301QEA |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | 2.6 A SWITCHING REGULATOR, 173 kHz SWITCHING FREQ-MAX, CDIP16 |
| 封装： | CERAMIC, DIP-16 |
| 文件页数： | 5/33页 |
| 文件大小： | 1016K |
| 代理商： | 5962-9650301QEA |
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LM2595 Series Buck Regulator Design Procedure (Adjustable Output)
(Continued)
PROCEDURE (Adjustable Output Voltage Version)
EXAMPLE (Adjustable Output Voltage Version)
Procedure continued on next page.
Example continued on next page.
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 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 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.
5. Catch Diode Selection (D1)
A. Refer to the table shown in
Figure 11 Schottky diodes pro-
vide the best performance, and in this example a 3A, 40V,
1N5822 Schottky diode would be a good choice. The 3A di-
ode rating is more than adequate and will not be over-
stressed even for a shorted output.
6. Input Capacitor (C
IN)
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 12 the DC load current. The capacitor manufacturers
data sheet must be checked to assure that this current rating
is not exceeded. The curve shown in
Figure 13 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.
se caution when using a high dielectric constant ceramic ca-
pacitor for input bypassing, because it may cause severe
ringing at the V
IN pin.
For additional information, see section on input capaci-
tors in application information section.
6. Input Capacitor (C
IN)
The important parameters for the Input capacitor are the in-
put voltage rating and the RMS current rating. With a nominal
input voltage of 28V, an aluminum electrolytic aluminum elec-
trolytic capacitor with a voltage rating greater than 42V (1.5 x
V
IN) would be needed. Since the the next higher capacitor
voltage rating is 50V, a 50V capacitor should be used. The
capacitor voltage rating of (1.5 x V
IN) is a conservative guide-
line, and can be modified somewhat if desired.
The RMS current rating requirement for the input capacitor of
a buck regulator is approximately 12 the DC load current. In
this example, with a 1A load, a capacitor with a RMS current
rating of at least 500 mA is needed.
The curves shown in
Figure 13 can be used to select an ap-
propriate input capacitor. From the curves, locate the 50V
line and note which capacitor values have RMS current rat-
ings greater than 500 mA. Either a 100 F or 120 F, 50V ca-
pacitor could be used.
For a through hole design, a 120 F/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 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 rting (see Application Information or in-
put 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 or later)
is available on a 312" diskette for IBM compatible computers.
www.national.com
13
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