The advanced fast-response voltage-mode control scheme of the converters allows the use of tiny ceramic capacitors with a typical value of 10 μF to 22 μF, without having large output-voltage under- and overshoots during heavy load transients. Ceramic capacitors with low ESR values result in lowest output-voltage ripple, and TI therefore recommends them. The output capacitor requires either X7R or X5R dielectric. TI does not recommend Y5V and Z5U dielectric capacitors because of their wide variation in capacitance.

If using ceramic output capacitors, the capacitor rms ripple-current rating always meets the application requirements. The rms ripple current calculation is:

Equation 6.

At nominal load current, the inductive converters operate in PWM mode and the overall output voltage ripple is the sum of the voltage spike caused by the output capacitor ESR, plus the voltage ripple caused by charging and discharging the output capacitor:

Equation 7.

where

• The highest output-voltage ripple occurs at the highest input voltage, V_IN.

At light load currents, the converters operate in power-save mode and the output-voltage ripple depends on the output-capacitor value. The internal comparator delay and the external capacitor set the output-voltage ripple. Higher output capacitors like 22 μF values minimize the voltage ripple in PFM mode and tighten dc output accuracy in PFM mode.