LM2595

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SNVS122B – MAY 1999 – REVISED APRIL 2013

Solid tantalum capacitors have a much better ESR spec for cold temperatures and are recommended for

temperatures below

−25°C.

Figure 27. Capacitor ESR vs Capacitor Voltage Rating (Typical Low ESR Electrolytic Capacitor)

CATCH DIODE

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 LM2595 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. Ultra-fast recovery diodes typically have reverse recovery times of 50 ns or less. Rectifiers such

as the 1N5400 series are much too slow and should not be used.

Figure 28. Capacitor ESR Change vs Temperature

INDUCTOR SELECTION

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 LM2595 (or any of the Simple Switcher family) can be used for both continuous or discontinuous modes of

operation.

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