CM2596 Datasheet, PDF (8/12 Pages) List of Unclassifed Manufacturers – 3A STEP DOWN VOLTAGE REGULATOR

CM2596
3A STEP DOWN VOLTAGE REGULATOR
APPLICATION INFORMATION
External component selector
Input Capacitors (Cin)
It is required that VIN must be bypassed with at least a 100uF electrolytic capacitor for stability. Also, it is strongly recommended
the capacitor’s leads must be short, wide and located near the regulator as possible. The important parameters for the capacitor
are the voltage rating and the RMS current rating. For a maximum ambient temperature of 40℃, a general guideline would be to
select a capacitor with a ripple current rating of approximately 50% of the DC load current. The capacitor voltage rating must be
at least 1.25 times greater than the maximum input voltage.
For low operating temperature range, for example, below -25℃, 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 (C_OUT)
An output capacitor is also required to filter the output voltage and is needed for loop stability. The capacitor should be located
near the CM2596 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 (220uF – 1000uF) will yield typically 50mV to 150mV of output ripple voltage, while
larger-value capacitors will reduce the ripple to approximately 20mV to 50mV.
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_IND).
Output Ripple Voltage = (△ I_IND) x (ESR of C_OUT)
Some capacitors called “high-frequency”, “low-inductance”, or “low-ESR” are recommended to use to further reduce the output
ripple voltage to 10mV or 20mV. 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
CM2596 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 better choice.
2005/03/04
Champion Microelectronic Corporation
Page 8