AMC2576

Copyright

© 2006 ADDtek Corp.

8

DD007_E

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DECEMBER 2006

APPLICATION INFORMATION

recommended the capacitor’s leads must be dept short, and located near the regulator as possible.

For low operating temperature range, for example, below -25°C, the input capacitor value may need to be larger. This

is due to the reason that the capacitance value of electrolytic capacitors decreases and the ESR increases with lower

temperatures and age. Paralleling a ceramic or solid tantalum capacitor will increase the regulator stability at cold

temperatures.

An output capacitor is also required to filter the output voltage and is needed for loop stability. The capacitor should

be located near the AMC2576 using short PC board traces. Low ESR types capacitors are recommended for low

output ripple voltage and good stability. Generally, low value or low voltage (less than 12V) electrolytic capacitors

usually have higher ESR numbers. For example, the lower capacitor values (220µF–1000µF) will yield typically 50

mV to 150 mV of output ripple voltage, while larger-value capacitors will reduce the ripple to approximately 20 mV

to 50 mV.

The amount of output ripple voltage is primarily a function of the ESR (Equivalent Series Resistance) of the output

capacitor and the amplitude of the inductor ripple current (

∆I

Output Ripple Voltage = (

∆I

Some capacitors called “high-frequency,” “low-inductance,” or “low-ESR.” are recommended to use to further reduce

the output ripple voltage to 10 mV or 20 mV. However, very low ESR capacitors, such as Tantalum capacitors, should

be carefully evaluated.

Catch Diode

This diode is required to provide a return path for the inductor current when the switch is off. It should be located

close to the AMC2576 using short leads and short printed circuit traces as possible.

To satisfy the need of fast switching speed and low forward voltage drop, Schottky diodes are widely used to provide

the best efficiency, especially in low output voltage switching regulators (less than 5V).

Besides, fast-Recovery,

high-efficiency, or ultra-fast recovery diodes are also suitable. But some types with an abrupt turn-off characteristic

may cause instability and EMI problems. A fast-recovery diode with soft recovery characteristics is a better choice.