When the EN pin voltage rises above the enable threshold voltage (typically 1.2 V), the controller enters the start-up sequence. The internal LDO regulator starts immediately and regulates to 5 V at the VREG pin. The controller then uses the first 250 μs to calibrate the switching frequency setting resistance attached to the RF pin and stores the switching frequency code in internal registers. However, switching is inhibited during this phase. In the second phase, an internal DAC starts ramping up the reference voltage from 0 V to 0.6 V. Depending on the MODE pin setting, the ramping up time varies from 0.7 ms to 5.6 ms. Smooth and constant ramp-up of the output voltage is maintained during start-up regardless of load current.