8.2.2.1 Input Capacitor C_IN1, C_IN2 Selection (Buck Controllers)

It is good analog design practice to place input capacitors near the inputs of the device in order to ensure a low impedance input supply. 10μF to 22μF of capacitance for each buck converter is adequate for most applications, and should be placed within 100mils (0.01in, or 2.54mm) of the IN1 and IN2 pins to minimize the effects of pulsed current switching noise on the soft-start circuitry during the first ~1V of output voltage ramp. Low ESR capacitors also help to minimize noise on the supply line. The minimum value of capacitance can be estimated using Equation 4:

Equation 4.

Note that the capacitors must be able to handle the RMS current in continuous conduction mode, which can be calculated using Equation 5:

Equation 5.