The start-up waveform is shown in Figure 2-15. The top trace shows ENA, and the bottom trace shows Vout. Initially, the output is inhibited by using a jumper at JP1 to tie EN to GND. When the jumper is removed, ENA is released. When the ENA voltage reaches the enable-threshold voltage of 1.06 V, the start-up sequence begins and the internal reference voltage begins to ramp up at the internally set rate towards 1.221 V and the output voltage ramps up to the externally set value of 5 V. The start-up waveform is the same for both the TPS5430EVM-173 and the TPS5431EVM-173.

Figure 2-15 TPS5430 and TPS5431 Start-Up