The TPS54550EVM-158 start-up waveforms are shown in Figure 4-8. The top trace shows V_IN whereas the bottom trace shows OUT. Vin charges up from 0 V toward 12 V. When the input voltage reaches the internally set UVLO threshold voltage, the slow-start sequence begins. After a delay, the internal reference begins to ramp up linearly at the internally set slow-start rate towards 0.891 V, and the output ramps up toward the set voltage of 5 V. The output may be inhibited by using a jumper at JP1 to tie EN to GND. When the jumper is removed, EN is released and the slow-start voltage begins to ramp up at the internally set rate. When the EN voltage reaches the enable-threshold voltage of 1.06 V, the start-up sequence begins as described previously.

Figure 4-8 Power Up, OUT Relative to V_IN