The feedback capacitor, C_FB, shown in Figure 8-2 is required for stability. For a parallel combination of R₁ and R₂ equal to 250 kΩ, any value from 3 pF to 1 nF can be used. Fixed-voltage versions have an internal 30-pF feedback capacitor that is quick-charged at start-up. The adjustable version does not have this quick-charge circuit, so values below 5 pF must be used to ensure fast start-up; values above 47 pF can be used to implement an output voltage soft-start. Larger value capacitors also improve noise slightly. The TPS79901-Q1 device is stable in unity-gain configuration (OUT tied to FB) without C_FB.