The output voltage is set by an external resistor divider according to Equation 4:
R2 must not be higher than 100 kΩ to achieve high efficiency at light load while providing acceptable noise sensitivity. Equation 5 shows how to compute the value of the feedforward capacitor for a given R2 value. For the recommended 100k value for R2, a 120-pF feedforward capacitor is used.
For the fixed output voltage versions, connect the FB pin to the output. R1, R2, and C3 are not needed. The fixed output voltage devices have an internal feedforward capacitor.