8.1.1.1 Input and Output Capacitor Requirements (C_IN and C_OUT)

The TPS7A54 is designed and characterized for operation with ceramic capacitors of 47 µF or greater (22 µF or greater of capacitance) at the output and 10 µF or greater (5 µF or greater of capacitance) at the input. Use at least a 47-µF capacitor at the input to minimize input impedance. Place the input and output capacitors as near as practical to the respective input and output pins in order to minimize trace parasitics. If the trace inductance from the input supply to the TPS7A54 is high, a fast current transient can cause V_IN to ring above the absolute maximum voltage rating and damage the device. This situation can be mitigated by additional input capacitors to dampen and keep the ringing below the device absolute maximum ratings.

A combination of multiple output capacitors boosts the high-frequency PSRR. The combination of one 0805-sized, 47-µF ceramic capacitor in parallel with two 0805-sized, 10-µF ceramic capacitors with a sufficient voltage rating, in conjunction with the PSRR boost circuit, optimizes PSRR for the frequency range of 400 kHz to 700 kHz, a typical range for dc/dc supply switching frequency. This 47-µF || 10-µF || 10-µF capacitor combination also makes certain that at high input voltage and high output voltage configurations, the minimum effective capacitance is met. Many 0805-sized, 47-µF ceramic capacitors have a voltage derating of approximately 60% to 80% at 5.0 V, so the addition of the two 10-µF capacitors makes sure that the capacitance is at or above 22 µF.