8.2.2.4 Input Capacitor Selection

The input current of a buck converter is pulsating. Therefore, a low ESR input capacitor is required to prevent large voltage transients at the source but still providing peak currents to the device. The recommended Capacitance value for most applications is 2 x 10 µF, split between the VIN1 and VIN2 inputs and placed as close as possible to these pins and PGND pins. If additional capacitance is needed, it can be added as bulk capacitance. To ensure proper operation, the effective capacitance at the VIN pins must not fall below 2 x 5 µF.

Low ESR multilayer ceramic capacitors are recommended for best filtering. Increasing with input voltage, the dc bias effect reduces the nominal capacitance value significantly. To decrease input ripple current further, larger values of input capacitors can be used.