LM2576, LM2576HV
www.ti.com
SNVS107C –JUNE 1999–REVISED APRIL 2013
(For Continuous Mode Operation)
PROCEDURE (Adjustable Output Voltage Versions)
EXAMPLE (Adjustable Output Voltage Versions)
2. Inductor Selection (L1)
2. Inductor Selection (L1)
A. Calculate the inductor Volt • microsecond constant, E • T (V • μs), A. Calculate E • T (V • μs)
from the following formula:
B. E • T = 115 V • μs
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 27.
C. ILOAD(Max) = 3A
D. Inductance Region = H150
E. Inductor Value = 150 μH Choose from AIEpart #415-0936Pulse
Engineering part #PE-531115, or Renco part #RL2445.
C. On the horizontal axis, select the maximum load current.
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 Table 2. Part numbers
are listed for three inductor manufacturers. The inductor chosen
must be rated for operation at the LM2576 switching frequency (52
kHz) and for a current rating of 1.15 × ILOAD. For additional inductor
information, see INDUCTOR SELECTION.
3. Output Capacitor Selection (COUT
)
3. Output Capacitor Selection (COUT)
A. The value of the output capacitor together with the inductor
defines the dominate pole-pair of the switching regulator loop. For
stable operation, the capacitor must satisfy the following
requirement:
However, for acceptable output ripple voltage select
OUT ≥ 680 μF
C
COUT = 680 μF electrolytic capacitor
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 select a capacitor rate for a higher voltage than would
normally be needed.
4. Catch Diode Selection (D1)
4. Catch Diode Selection (D1)
A. The catch-diode current rating must be at least 1.2 times greater A. For this example, a 3.3A current rating is adequate.
than the maximum load current. Also, if the power supply design
B. Use a 30V 31DQ03 Schottky diode, or any of the suggested fast-
must withstand a continuous output short, the diode should have a
recovery diodes in Table 1.
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 Table 1.
B. The reverse voltage rating of the diode should be at least 1.25
times the maximum input voltage.
5. Input Capacitor (CIN
An aluminum or tantalum electrolytic bypass capacitor located close A 100 μF aluminum electrolytic capacitor located near the input and
to the regulator is needed for stable operation. ground pins provides sufficient bypassing.
)
5. Input Capacitor (CIN)
To further simplify the buck regulator design procedure, TI is making available computer design software to be
used with the SIMPLE SWITCHER line of switching regulators. Switchers Made Simple (Version 3.3) is
available on a (3½″) diskette for IBM compatible computers from a TI office in your area.
Copyright © 1999–2013, Texas Instruments Incorporated
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