LM2576BM
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.
OUTPUT CAPACITOR COUT
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 DIODE 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)
7/9
TGS [ Tiger Electronic Co.,Ltd ]
