The input capacitor is the low-impedance energy source for the converter, which helps provide stable operation. Because the buck converter has a pulsating input current, a low ESR ceramic input capacitor is required for best input voltage filtering to minimize input voltage spikes. Place the capacitor between VIN and GND pins and as close as possible to those pins.

For most applications, a minimum effective input capacitance of 3 µF is sufficient, though a larger value reduces input current ripple and is recommended. When operating from a high impedance source, TI recommends a larger input buffer capacitor ≥10 µF to avoid voltage drops during start-up and load transients. Additionally, small de-coupling capacitors can also be used in case of noise at the input if the device. The input capacitor can be increased without any limit for better input voltage filtering.

Table 8-7 shows a list of recommended capacitors.