7.3.5 Start-Up Sequence and Timing

After input power is applied, the 5-V onboard regulator comes up. Once this regulator comes up, the device goes through a period where it samples the impedance at the COMP pin and determines the short circuit protection threshold voltage, by placing 400 mV on the COMP pin for approximately 1 ms. During this time, the current is measured and compared against internal thresholds to select the short circuit protection threshold. After this, the COMP pin is brought low for 1 ms. This ensures that the feedback loop is preconditioned at start-up and no sudden output rise occurs at the output of the converter when the converter is allowed to start switching. After these initial two milliseconds, the internal soft-start circuitry is engaged and the converter is allowed to start. See Figure 13.

Figure 13. Start-Up Sequence