The output voltage of the LM6x4xx is externally adjustable using a resistor divider network. Two divider networks for two recommended output voltages are found in Table 9-2. The divider network is comprised of the top and bottom feedback resistors, R_FBT and R_FBB, and closes the loop between the output voltage and the converter. The converter regulates the output voltage by holding the voltage on the FB pin equal to the internal reference voltage, V_FB = 1 V. The total resistance of the divider is a compromise between excessive noise pickup and excessive loading of the output. Lower resistance values reduce noise sensitivity but also reduce the light-load efficiency. The recommended value for R_FBT is 100 kΩ with a maximum value of 1 MΩ. If 1 MΩ is selected for R_FBT, then a feedforward capacitor C_FF must be used across this resistor to provide adequate loop phase margin (see Section 9.2.2.9). Once R_FBT is selected, Equation 1 is used to select R_FBB. For this 5-V example, R_FBT = 100 kΩ and R_FBB = 24.9 kΩ.