ZHCSI09S June 2010 – August 2018 TPS65911
TI recommends ceramic capacitors with low ESR values because they provide the lowest output voltage ripple. The output capacitor requires either an X7R or X5R rating. Y5V and Z5U capacitors, aside from the wide variation in capacitance over temperature, become resistive at high frequencies. At light load currents, the converter operates in PFM mode and the output voltage ripple is dependent on the output-capacitor value and the PFM peak inductor current. Higher output-capacitor values minimize the voltage ripple in PFM mode. To achieve specified regulation performance and low output voltage ripple, the DC-bias characteristic of ceramic capacitors must be considered. The effective capacitance of ceramic capacitors drops with increasing DC-bias voltage. For the output capacitors of the BUCK converters, TI recommends placing small ceramic capacitors between the inductor and load with many vias to the PGND plane. This solution typically provides the smallest and lowest-cost solution available for the converters. The output capacitance must equal to or greater than the minimum capacitance listed for VDD1, VDD2, and VIO (assuming quality layout techniques are followed). The recommended value is 10 µF.