The type 3 ripple injection network allows the use of small, low ESR, ceramic output capacitors, while the ripple injection network provides the proper signal to the regulation comparator.

One way to select the value of output capacitance is with the help of Equation 33. This equation sizes the output capacitor based on a specified load current transient and output voltage transient.

Where:

• ΔV = Change in output voltage during load transient.
• ΔI_L = inductor ripple current from Equation 27

For this example we specify ΔV = 50 mV for a full load transient of 300 mA. I_peak is calculated using Equation 28. Arrive at C_OUT greater than about 17 μF. With voltage coefficients of ceramic capacitors taken in consideration, a 22-μF, 25-V rated capacitor with X7R dielectric is selected. More output capacitance can be used to provide smaller load transients or lower output voltage ripple. Keep in mind that the minimum output capacitance must be > 2.2 μF. Equation 34 can be used to estimate the switching frequency output ripple, assuming that the output capacitor ESR is not dominant.

Where:

• V_r = peak-to-peak output voltage ripple at the switching frequency
• ΔI_L = inductor ripple current from Equation 27.