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 DCV010505 device:

• V_OUT = 5 V
• I_OUT = 0.2 A
• At full output power, the load resistor is 25 Ω
• 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 × 25 = 25 µs
• V_DIS = V_O(1 – EXP(–t_DIS / τ))
• V_DIS = 2.5 mV

By contrast, the voltage dropped because of ESR:

• V_ESR = I_LOAD × ESR
• V_ESR = 0.2 × 0.1 = 20 mV
• Ripple voltage = 22.5 mV