The TPS563300 device requires an input decoupling capacitor and, depending on the application, a bulk input capacitor. The typical recommended value for the decoupling capacitor is 10 μF, and an additional 0.1-µF capacitor from the VIN pin to ground is recommended to provide high frequency filtering.

The value of a ceramic capacitor varies significantly over temperature and the amount of DC bias applied to the capacitor. X5R and X7R ceramic dielectrics are recommended because they have a high capacitance-to-volume ratio and are fairly stable over temperature. The capacitor must also be selected with the DC bias taken into account. The effective capacitance value decreases as the DC bias increases.

The capacitor voltage rating needs to be greater than the maximum input voltage. The capacitor must also have a ripple current rating greater than the maximum input current ripple of the TPS563300. The input ripple current can be calculated using Equation 20.

Equation 20.

For this example design, two TDK CGA5L1X7R1H106K160AC (10-μF, 50-V, 1206, X7R) capacitors have been selected. The effective capacitance under input voltage of 24 V for each one is 3.45 μF. The input capacitance value determines the input ripple voltage of the converter. The input voltage ripple can be calculated using Equation 21. Using the design example values, I_{OUT_MAX} = 3 A, C_{IN_EFF} = 2 × 3.45 = 6.9 μF, and f_SW = 500 kHz, yields an input voltage ripple of 222 mV and a RMS input ripple current of 1.22 A.

Equation 21.

where

• R_{ESR_MAX} is the maximum series resistance of the input capacitor (approximately 1.5 mΩ of two capacitors in paralleled).