TPS60403 power up sequence

In general the startup of the part happens faster than a switcher startup and the part will start operation at the moment the input voltage is in the range of 1.5V with 20mA load. Attached you can find a measurement of the startup into an electronic load of 20mA. I set the input voltage to start in 10ms. Green = VIN, Blue = VOUT, Red = IOUT. I also had a look on 200 Ohm load and also then the startup is within 10ms.

But be careful with the expected output voltage. Figure 15 on page 10 gives a estimation of the output voltage with 5V input voltage over output current. In addition, you can calculate the worst case scenario with the output resistance given in the datasheet. On page 3 you can calculate the worst case output voltage with 20mA output current using the 15 Ohm output resistance from the electrical specification table. Using the standard capacitors of 1uF, you will get a worst case output voltage of -4.7V with 5V input voltage. With 15 Ohm output impedance and 20mA output current, the output voltage value will always be 300mV smaller than the input voltage value.

The attached file shows that the voltage on the output is in the range of 4.7V.