The TPS7H4010-SEP device requires high-frequency ceramic input decoupling capacitors. Depending on the application, a bulk input capacitor can also be added. The typical recommended ceramic decoupling capacitors include one small 0.1-µF to 1-µF capacitor, and one large 10-µF to 22-µF capacitor. TI recommends high-quality ceramic type X5R or X7R capacitors. The voltage rating must be greater than the maximum input voltage. As a general rule, to compensate the derating TI recommends a voltage rating of twice the maximum input voltage.

It is very important in buck regulator applications to place the small decoupling capacitor right next to the PVIN and PGND pins. This capacitor is used to bypass the high frequency switching noise by providing a return path of the noise. It prevents the noise from spreading to wider area of the board. The large bypass ceramic capacitor must also be as close as possible to the PVIN and PGND pins.

Additionally, some bulk capacitance may be required, especially if the TPS7H4010-SEP circuit is not located within approximately 2 inches from the input voltage source. This capacitor is used to provide damping to the voltage spike due to the lead inductance of the cable. The optimum value for this capacitor is four times the ceramic input capacitance with ESR close to the characteristic impedance of the LC filter formed by your input inductance and your ceramic input capacitors. It is not critical that the electrolytic filter be at the optimum value for damping, but it must be rated to handle the maximum input voltage including ripple voltage.

For this design, two 10-µF, X7R dielectric capacitors rated for 50 V are used for the input decoupling capacitance, and a capacitor with a value of 0.47 µF for high-frequency filtering.