CM2500 Datasheet, PDF (8/11 Pages) Champion Microelectronic Corp. – WIDE INPUT 2A STEP DOWN CONVERTER

CM2500
WIDE INPUT 2A STEP DOWN CONVERTER
STEP 2. Set the zero fZ1 at 1/4 of the crossover frequency.
If RCOMP is less than 15kΩ, the equation for CCOMP is:
If RCOMP is limited to 15kΩ, then the actual cross over
frequency is 3.4 / (VOUTCOUT). Therefore:
STEP 3. If the output capacitor’s ESR is high enough to
cause a zero at lower than 4 times the crossover frequency,
an additional compensation capacitor CCOMP2 is required.
The condition for using CCOMP2 is:
RESRCOUT
And the proper value for CCOMP2 is:
Though CCOMP2 is unnecessary when the output capacitor
has sufficiently low ESR, a small value CCOMP2 such as
100pF may improve stability against PCB layout parasitic
effects. Table 2 shows some calculated results based on the
compensation method above.
Table 2. Typical Compensation for Different
Output Voltages and Output Capacitors
VOUT
2.5V
3.3V
5V
2.5V
3.3V
5V
2.5V
3.3V
5V
COUT
22μF Ceramic
22μF Ceramic
22μF Ceramic
47μF SP Cap
47μF SP Cap
47μF SP Cap
470μF/6.3V/30mΩ
470μF/6.3V/30mΩ
470μF/10V/30mΩ
RCOMP
8.2kΩ
12kΩ
15kΩ
15kΩ
15kΩ
15kΩ
15kΩ
15kΩ
15kΩ
CCOMP
2.2nF
1.5nF
1.5nF
1.5nF
1.8nF
2.7nF
15nF
22nF
27nF
CCOMP2
None
None
None
None
None
None
1nF
1nF
None
2008/04/15 Rev1.0
Champion Microelectronic Corporation
Page 8