Input capacitor should have enough ripple current rating to absorb input switching ripple current. The worst case RMS ripple current is half of the output when duty cycle is 0.5 in forward buck mode, or reverse boost mode. If the converter does not operate at 50% duty cycle, then the worst case capacitor RMS current occurs where the duty cycle is closest to 50% and can be estimated by Equation 14:

A combination of ceramic and bulk capacitors should be used to provide a short path for high di/dt current and to reduce the voltage ripple. Ceramic capacitors should be placed close to the switching half-bridge. Given total bulk input capacitance, it is recommended to distribute equally on either side of R_{AC_SNS}. The complete schematic is a good starting point for input capacitor for typical applications.