The following example shows that increasing the capacitance has a much smaller effect on the output ripple voltage than does reducing the value of the ESR for the filter capacitor.

To calculate the output ripple for a DCP010505 device:

• V_OUT = 5 V
• I_OUT = 0.2 A
• At full output power, the load resistor is 25 Ω
• Ceramic output capacitor of 1 μF, ESR of 0.1 Ω
• Capacitor discharge time 1% of 800 kHz (ripple frequency)

t_DIS = 0.0125 μs

τ = C × R_LOAD

τ = 1 × 10^-6 × 12.5 = 12.5 μs

V_DIS = V_O(1 – EXP(–t_DIS / τ))

V_DIS = 5 mV

By contrast, the voltage dropped because of ESR:

V_ESR = I_LOAD × ESR

V_ESR = 20 mV

Ripple voltage = 25 mV