CM2500 Datasheet, PDF (7/11 Pages) Champion Microelectronic Corp. – WIDE INPUT 2A STEP DOWN CONVERTER

CM2500
WIDE INPUT 2A STEP DOWN CONVERTER
INPUT CAPACITOR
The input capacitor needs to be carefully selected to
maintain sufficiently low ripple at the supply input of the
converter. A low ESR capacitor is highly recommended.
Since large current flows in and out of this capacitor during
switching, its ESR also affects efficiency. The input
capacitance needs to be higher than 10μF. The best choice
is the ceramic type; however, low ESR tantalum or
electrolytic types may also be used provided that the RMS
ripple current rating is higher than 50% of the output current.
The input capacitor should be placed close to the IN and G
pins of the IC, with the shortest traces possible. In the case
of tantalum or electrolytic types, they can be further away if a
small parallel 0.1μF ceramic capacitor is placed right next to
the IC.
OUTPUT CAPACITOR
The output capacitor also needs to have low ESR to keep
low output voltage ripple. The output ripple voltage is:
STABILITY COMPENSATION
The feedback loop of the IC is stabilized by the components at
the COMP pin, as shown in Figure 5. The DC loop gain of the
system is determined by the following equation:
where IOUTMAX is the maximum output current, KRIPPLE is
the ripple factor, RESR is the ESR of the output capacitor,
fSW is the switching frequency, L is the inductor value, and
COUT is the output capacitance. In the case of ceramic
output capacitors, RESR is very small and does not
contribute to the ripple. Therefore, a lower capacitance value
can be used for ceramic capacitors. In the case of tantalum
or electrolytic capacitors, the ripple is dominated by RESR
multiplied by the ripple current. In that case, the output
capacitor is chosen to have sufficiently low ESR.
For ceramic output capacitors, typically choose a
capacitance of about 22μF. For tantalum or electrolytic
capacitors, choose a capacitor with less than 50mΩ ESR.
RECTIFIER DIODE
Use a Schottky diode as the rectifier to conduct current when
the High-Side Power Switch is off. The Schottky diode must
have a current rating higher than the maximum output
current and a reverse voltage rating higher than the
maximum input voltage.
2008/04/15 Rev1.0
Champion Microelectronic Corporation
Page 7