A precision 1.0-V reference voltage (V_REF) is used to maintain a tightly regulated output voltage over the entire operating temperature range. The output voltage is set by a resistor divider from V_OUT to the FB pin. It is recommended to use 1% tolerance resistors with a low temperature coefficient for the FB divider. Select the bottom-side resistor R_FBB for the desired divider current and use Equation 1 to calculate top-side resistor R_FBT. The recommend range for R_FBT is 10 kΩ to 100 kΩ. A lower R_FBT value can be used if pre-loading is desired to reduce V_OUT offset in PFM operation. Lower R_FBT reduces efficiency at very light load. Less static current goes through a larger R_FBT and can be more desirable when light-load efficiency is critical. However, R_FBT larger than 1 MΩ is not recommended because it makes the feedback path more susceptible to noise. Larger R_FBT values require more carefully designed feedback path trace from the feedback resistors to the feedback pin of the device. The tolerance and temperature variation of the resistor divider network affect the output voltage regulation.

Figure 8-2 Output Voltage Setting

Equation 1.