Fixed voltage versions of the TPS799-Q1 use a quick-start circuit to fast-charge the noise-reduction capacitor, C_NR, if present (see Figure 7-1). This circuit allows the combination of very low output noise and fast start-up times. The NR pin is high impedance so a low leakage C_NR capacitor must be used; most ceramic capacitors are appropriate in this configuration.

For the fastest start-up, apply V_IN first, then drive the enable pin (EN) high. If EN is tied to IN, start-up is somewhat slower. The quick-start switch is closed for approximately 135 μs. To ensure that C_NR is fully charged during the quick-start time, a 0.01 μF or smaller capacitor must be used.