C3: The capacitor on the V_CC output provides not only noise filtering and stability, but also prevents false triggering of the V_CC UVLO at the buck switch on and off transitions. For this reason, C3 must be no smaller than 0.1 µF.

C4: The recommended value is 0.022 µF for C4 because this value is appropriate in the majority of applications. A high-quality ceramic capacitor, with low ESR is recommended because C4 supplies the surge current to charge the buck switch gate at turn-on. A low ESR also ensures a quick recharge during each off-time. At minimum VIN when the on-time is at maximum, C4 can possibly not fully recharge at start-up during each 300-ns off-time. This failure to recharge results from the circuit being unable to complete the start-up and achieve output regulation. This condition can occur when the frequency is intended to be low (for example, R_ON = 500 kΩ). In this case, increase C4 to maintain sufficient voltage across the buck switch driver during each on-time.