ZHCSJO3 May 2019 LMR34215-Q1
In some cases a feed-forward capacitor can be used across RFBT to improve the load transient response or improve the loop-phase margin. This is especially true when values of RFBT > 100 kΩ are used. Large values of RFBT, in combination with the parasitic capacitance at the FB pin, can create a small signal pole that interferes with the loop stability. A CFF can help to mitigate this effect. can be used to estimate the value of CFF. The value found with Equation 9 is a starting point; use lower values to determine if any advantage is gained by the use of a CFF capacitor. The application report Optimizing Transient Response of Internally Compensated DC-DC Converters with Feed-forward Capacitor is helpful when experimenting with a feed-forward capacitor.