JAJSFE5C October 2009 – May 2018 TPS65720 , TPS65721
PRODUCTION DATA.
The advanced Fast Response voltage mode control scheme of the step-down converter allows the use of small ceramic capacitors with a typical value of 10 μF, without having large output voltage under and overshoots during heavy load transients. Ceramic capacitors having low ESR values result in lowest output voltage ripple and are therefore recommended. For an inductor value of 3.3 μH, an output capacitor with 4.7 μF can be used. Refer to recommended components.
If ceramic output capacitors are used, the capacitor RMS ripple current rating will always meet the application requirements. Just for completeness the RMS ripple current is calculated by 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, as calculated by Equation 7:
Where the highest output voltage ripple occurs at the highest input voltage Vin.
At light load currents the converter operates in power save mode and the output voltage ripple is dependent on the output capacitor value. The output voltage ripple is set by the internal comparator delay and the external capacitor. The typical output voltage ripple is less than 1% of the nominal output voltage.