A feedforward capacitor, CFF on the order of tens of picofarads, is used to improve phase margin and transient response of circuits which have output capacitors with low ESR. Since this CFF capacitor can conduct noise from the output of the circuit directly to the FB node of the IC, a 4.99-kΩ resistor, RFF, must be placed in series with CFF. If the ESR zero of the output capacitor is below 200 kHz, no CFF must be used.
If output voltage is less than 2.5 V, CFF has little effect, so it can be omitted. If output voltage is greater than 14 V, CFF must be used cautiously since it can easily introduce too much gain at higher frequencies.
If 1 MΩ is selected for RFBT, then a feedforward capacitor CFF must be used.