Considering the loop stability and the effect of the internal parasitic parameters, choose a crossover frequency less than 40 kHz, without considering the feed-forward capacitor. A simple estimation for the crossover frequency without feed-forward capacitor C8 is shown in Equation 2, assuming C_OUT has small ESR.

Equation 2.

Depending on V_OUT, if the output capacitor, C_OUT, is dominated by low-ESR (ceramic types) capacitors, a low phase margin could result. To improve the phase boost, an external feed-forward capacitor, C8, can be added in parallel with R2. C8 is chosen such that phase margin is boosted at the crossover frequency.

C8 is calculated in Equation 3:

Equation 3.

For this design, C8 = 75 pF. C8 is not needed when C_OUT has high ESR, and C8 calculated from Equation 3 should be reduced with medium ESR. Use Table 1-3 as a starting point.