A precision 0.8-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. TI recommends 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 the top-side resistor, R_FBT. The recommended range for R_FBT is 10 k? to 100 k?. A lower R_FBT value can be used if pre-loading is desired to reduce the V_OUT offset in PFM operation. Lower R_FBT values reduce efficiency at very light load. Less static current goes through a larger R_FBT value and can be more desirable when light-load efficiency is critical. However, R_FBT values larger than 1 M? are not recommended because they make the feedback path more susceptible to noise. Larger R_FBT values require a 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 7-2 Output Voltage Setting

Equation 1.