LM2576HVS-ADJ National Semiconductor, LM2576HVS-ADJ Datasheet - Page 13

• Manufacturer Part Number: LM2576HVS-ADJ
• Description: Voltage Regulator IC
• Manufacturer: National Semiconductor

Specifications of LM2576HVS-ADJ

• Input Voltage: 60V
• No. Of Pins: 3
• Peak Reflow Compatible (260 C): No
• Termination Type: SMD
• Supply Voltage Max: 60V
• Leaded Process Compatible: No
• Package / Case: 3-TO-263
• Output Current Max: 3A
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

LM2576 Series Buck Regulator Design Procedure
2. Inductor Selection (L1)
A. Calculate the inductor Volt • microsecond constant,
E
B. Use the E • T value from the previous formula and
match it with the E • T number on the vertical axis of the
Inductor Value Selection Guide shown in Figure 7 .
C. On the horizontal axis, select the maximum load cur-
rent.
D. Identify the inductance region intersected by the E • T
value and the maximum load current value, and note the
inductor code for that region.
E. Identify the inductor value from the inductor code, and
select an appropriate inductor from the table shown in
Figure 9 . Part numbers are listed for three inductor manu-
facturers. The inductor chosen must be rated for opera-
tion at the LM2576 switching frequency (52 kHz) and for a
current rating of 1.15 x I
formation, see the inductor section in the application hints
section of this data sheet.
3. Output Capacitor Selection (C
A. The value of the output capacitor together with the in-
ductor defines the dominate pole-pair of the switching
regulator loop. For stable operation, the capacitor must
satisfy the following requirement:
The above formula yields capacitor values between 10 µF
and 2200 µF that will satisfy the loop requirements for
stable operation. But to achieve an acceptable output
ripple voltage, (approximately 1% of the output voltage)
and transient response, the output capacitor may need to
be several times larger than the above formula yields.
B. The capacitor’s voltage rating should be at last 1.5
times greater than the output voltage. For a 10V regulator,
a rating of at least 15V or more is recommended. Higher
voltage electrolytic capacitors generally have lower ESR
numbers, and for this reason it may be necessary to se-
lect a capacitor rate for a higher voltage than would nor-
mally be needed.
4. Catch Diode Selection (D1)
A. The catch-diode current rating must be at least 1.2
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 LM2576. The most stressful
condition for this diode is an overload or shorted output.
See diode selection guide in Figure 8 .
B. The reverse voltage rating of the diode should be at
least 1.25 times the maximum input voltage.
5. Input Capacitor (C
An aluminum or tantalum electrolytic bypass capacitor lo-
cated close to the regulator is needed for stable opera-
tion.
PROCEDURE (Adjustable Output Voltage Versions)
• T (V
•
µs),
IN
)
LOAD
from
. For additional inductor in-
the
OUT
following
)
formula:
13
2. Inductor Selection (L1)
A. Calculate E • T (V • µs)
B. E • T = 115 V • µs
C. I
D. Inductance Region = H150
E. Inductor Value = 150 µH Choose from AIE part
# 415-0936 Pulse Engineering part # PE-531115, or
Renco part # RL2445.
3. Output Capacitor Selection (C
However, for acceptable output ripple voltage select
C
C
4. Catch Diode Selection (D1)
A. For this example, a 3.3A current rating is adequate.
B. Use a 30V 31DQ03 Schottky diode, or any of the sug-
gested fast-recovery diodes in Figure 8 .
5. Input Capacitor (C
A 100 µF aluminum electrolytic capacitor located near the
input and ground pins provides sufficient bypassing.
OUT
OUT
EXAMPLE (Adjustable Output Voltage Versions)
LOAD
= 680 µF electrolytic capacitor
680 µF
(Max) = 3A
(Continued)
IN
)
OUT
)
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