SNVS124C – NOVEMBER 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 26. 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 LM2596 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 27. 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 LM2596 (or any of the Simple Switcher family) can be used for both continuous or discontinuous modes of
operation.
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