LM2576BM

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temperatures up to 70°C, a current rating of 75% of the DC load current would be a good

choice for a conservative design. The capacitor voltage rating must be at least 1.25 times

greater than the maximum input voltage, and often a much higher voltage capacitor is

needed to satisfy the RMS current requirements.

An output capacitor is required to filter the output and provide regulator loop stability. Low

impedance or low ESR Electrolytic or solid tantalum capacitors designed for switching

regulator applications must be used. When selecting an output capacitor, the important

capacitor parameters are; the 100 kHz Equivalent Series resistance (ESR), the RMS ripples

current rating, voltage rating, and capacitance value. For the output capacitor, the ESR

value is the most important parameter. The output capacitor requires an ESR value that has

an upper and lower limit. For low output ripple voltage, a low ESR value is needed. This

value is determined by the maximum allow able output ripple voltage, typically 1% to 2% of

the output voltage. But if the selected capacitor’s ESR is extremely low, there is a

possibility of an unstable feedback loop, resulting in an oscillation at the output.

CATCH DI ODE D1

Buck regulators require a diode to provide a return path for the inductor current

when the switch turns off. This must be a fast diode and must be located close to the

LM2576BM using short leads and short printed circuit traces. Because of their very fast

switching speed and low forward voltage drop, Schottky diodes provide the best

performance, especially in low output voltage applications (5V and lower). Ultra fast

recovery, or High-Efficiency rectifiers are also a good choice, but some types with an

abrupt turnoff characteristic may cause instability or EMI problems.

INDUCTOR SELECTION L

All switching regulators have two basic modes of operation; continuous and discontinuous.

The difference between the two types relates to the inductor current, whether it is flowing

continuously, or if it drops to zero for a period of time in the normal switching cycle. Each

mode has distinctively different operating characteristics, which can affect the regulators

performance and requirements. Most switcher designs will operate in the discontinuous

mode when the load current is low.

The

LM2576BM (or any of the Simple Switcher family) can be used for both continuous and

discontinuous modes of operation. There is a formula for general applications:

(Note The unit of voltage is V, the unit of current is A)