SNVA406C May 2010 – January 2022 LM27402
9.7 Frequency Adjust Resistor, Rf
The LM27402 switching frequency can be adjusted from 200 kHz to 1.2 MHz using an external resistor labeled on the evaluation board as Rf. The frequency of the LM27402 evaluation board was selected to be 300 kHz. A 300-kHz switching frequency enables the LM27402 to deliver high currents by reducing the MOSFET related losses while maintaining the ability to achieve satisfactory transient response. To find the value of resistance needed for a given frequency, use the following equation: (fSW (kHz), Rf (k?)).
A value of 45.7 k? was chosen for the Rf resistor on the LM27402 evaluation board.