10.2.1 Input Capacitor Selection

Because of the pulsating input current nature of the buck converter, a low ESR input capacitor is required to prevent large voltage transients that can cause misbehavior of the device or interference in other circuits in the system.

For most applications, the input capacitor that is integrated into the TPS8269x should be sufficient. If the application exhibits a noisy or erratic switching frequency, experiment with additional input ceramic capacitance to find a remedy.

The TPS8269x uses a tiny ceramic input capacitor. When a ceramic capacitor is combined with trace or cable inductance, such as from a wall adapter, a load step at the output can induce ringing at the VIN terminal. This ringing can couple to the output and be mistaken as loop instability or can even damage the part. In this circumstance, additional "bulk" capacitance, such as electrolytic or tantalum, should be placed between the input of the converter and the power source lead to reduce ringing that can occur between the inductance of the power source leads and C_I.