LM2575 & LM2576
POWER MANAGEMENT
Applications Information - Buck Mode
LM2575 LM2576
L1
D1
330µH
3A
100µH
7A
CIN
68µF
120µF
COUT 330µF 1,000µF
The above component selections will be adequate for Schottky versus an ultra fast diode is efficiency. Schottkys
most applications for output currents from 250mA to 3A will provide approximately 4% to 5% improvement for
(LM2576) or 150mA to 1A (LM2575). Applications with VOUTS below 12V, whereas above 12V the difference will
VOUT below 5V or above 24V may require component become less significant. Breakdown rating must be in
adjustment for maximum performance; please contact excess of VIN for margin.
factory for application assistance.
4. Input Capacitor. The value shown will be adequate for
1. Device Selection. Select an appropriate device from most applications. Ripple voltage at the switching
the Ordering Information guide based upon voltage frequency is caused by the input capacitor supplying load
option and package.
current during the on time of the power switch. The use
of a low ESR switching type capacitor will minimize ripple
2. Thermal Conditions. Most applications will not require to an acceptable level.
a heatsink for the TO-220 package. Approximate power
dissipation is:
5. Layout. Use short connections with a central point
ground to prevent improper operation caused by stray
inductance and ground loops.
VO
VIN
VOIO VSAT
P =
+ 0.02VIN
VIN
6. Output Capacitor. Ripple voltage on VOUT is directly
related to the value of COUT and the internal resistance
ESR of COUT. Output noise can be lowered by increasing
COUT 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 COUT.
3. Catch Diode. If the output must be capable of a
sustained short, the IF 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.
12
www.semtech.com
SEMTECH [ SEMTECH CORPORATION ]
