LM2575 & LM2576
POWER MANAGEMENT
Applications Information - Buck Mode
LM2575
L
1
D
1
C
IN
C
OUT
330µH
3A
68µF
330µF
LM2576
100µH
7A
120µF
1,000µF
The above component selections will be adequate for
most applications for output currents from 250mA to 3A
(LM2576) or 150mA to 1A (LM2575). Applications with
V
OUT
below 5V or above 24V may require component
adjustment for maximum performance; please contact
factory for application assistance.
1. Device Selection.
Select an appropriate device from
the Ordering Information guide based upon voltage
option and package.
2. Thermal Conditions.
Most applications will not require
a heatsink for the TO-220 package. Approximate power
dissipation is:
P
=
V
O
V
O
I
O
V
SAT
+
0 .02 V
IN
V
IN
V
IN
Schottky versus an ultra fast diode is efficiency. Schottkys
will provide approximately 4% to 5% improvement for
V
OUTS
below 12V, whereas above 12V the difference will
become less significant. Breakdown rating must be in
excess of V
IN
for margin.
4. Input Capacitor.
The value shown will be adequate for
most applications. Ripple voltage at the switching
frequency is caused by the input capacitor supplying load
current during the on time of the power switch. The use
of a low ESR switching type capacitor will minimize ripple
to an acceptable level.
5. Layout.
Use short connections with a central point
ground to prevent improper operation caused by stray
inductance and ground loops.
6. Output Capacitor.
Ripple voltage on V
OUT
is directly
related to the value of C
OUT
and the internal resistance
ESR of C
OUT
. Output noise can be lowered by increasing
C
OUT
or by selecting a capacitor with a lower ESR. ESR
must be a minimum of 0.03W for the LM2576 or 0.07W
for the LM2575 to maintain stability, otherwise raise the
value of C
OUT
.
12
www.semtech.com
3. Catch Diode.
If the output must be capable of a
sustained short, the I
F
rating must be above 3A for the
LM2575 and 7A for the LM2576. The use of an ultra
fast diode with soft recovery characteristics or a Schottky
will be adequate. The major impact on the selection of a
ã
2001 Semtech Corp.
SEMTECH [ SEMTECH CORPORATION ]
