AMC2576
APPLICATION INFORMATION
Input Capacitors (CIN)
It is required that VIN must be bypassed with at least a 100µF electrolytic capacitor for stability. Also, it is strongly
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.
Output Capacitors (COUT
)
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 (∆IIND).
Output Ripple Voltage = (∆IIND) × (ESR of COUT
)
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.
Copyright © 2006 ADDtek Corp.
8
DD007_E -- DECEMBER 2006
ADDTEK [ ADDTEK CORP ]
