Input decoupling ceramic capacitors type X5R, X7R, or similar from VIN to PGND that are placed as close as possible to the IC are required. A total of at least 66 µF of capacitance is required and some applications can require a bulk capacitance. TI recommends at least 1 µF of bypass capacitance as close as possible to each VIN pin to minimize the input voltage ripple. A 1-µF capacitor must be placed as close as possible to VIN pins 6, 7, 14 and 15 on the same side of the board of the device to provide high frequency bypass to reduce the high frequency overshoot and undershoot on VIN and SW pins. The voltage rating of the input capacitor must be greater than the maximum input voltage. The capacitor must also have a ripple current rating greater than the maximum RMS input current. The RMS input current can be calculated using Equation 22.

For this example design, a ceramic capacitor with at least a 25-V voltage rating is required to support the maximum input voltage. Two 22-µF, 1210, X7R, 25-V, two 10-µF, 0805, X7S, 25-V, and two 1-μF, 0402 or 0603, X7R 25-V capacitors in parallel has been selected to be placed on both sides of the IC near VIN pins to PGND pins. Based on the capacitor manufacturer's website, the total ceramic input capacitance derates to 25 µF at the nominal input voltage of 12 V. Additional 100-µF ceramic capacitance and 220-µF aluminum electrolytic are also used to bypass long leads when connected a lab bench top power supply.

The input capacitance value determines the input ripple voltage of the regulator. The input voltage ripple can be calculated using Equation 23. The maximum input ripple occurs when operating nearest to 50% duty cycle. Using the nominal design example values of I_OUT(MAX) = 20 A, C_IN = 25 μF, and f_SW = 1000 kHz, the input voltage ripple with the 12-V nominal input is 61 mV and the RMS input ripple current with the 4.5-V minimum input is 8.3 A.