LM2575 datasheet(12/19 Pages) SEMTECH

12 / 19 page

ã 2001 Semtech Corp.

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LM2575 & LM2576

POWER MANAGEMENT

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

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:

SAT

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

Schottky versus an ultra fast diode is efficiency. Schottkys

will provide approximately 4% to 5% improvement for

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

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.

Applications Information - Buck Mode

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