SNVA432D March 2010 – January 2022 LM21305
This can be seen on the schematic as components RF and CF. There is a practical limit to the size of the resistor RF as the AVIN pin will draw a short 60-mA burst of current during start-up, and if RF is too large the resulting voltage drop can trigger the UVLO comparator. For the evaluation board, a 1-Ω resistor is used for RF ensuring that the UVLO will not be triggered after the part is enabled. A recommended 1-μF CF capacitor coupled with the 1-Ω resistor provides approximately 10 dB of attenuation at 500-kHz switching frequency.