For a successful design, the junction temperature of the device must be kept below the absolute maximum rating during both dynamic (start-up) and steady-state conditions. Dynamic power stresses often are an order of magnitude greater than the static stresses, so it is important to determine the right start-up time and inrush current limit required with system capacitance to avoid thermal shutdown during start-up.

The slew rate (SR) needed to achieve the desired output rise time can be calculated as:

The C_dVdt needed to achieve this slew rate can be calculated as:

Choose the nearest standard capacitor value as 5600 pF.

For this slew rate, the inrush current can be calculated as:

The average power dissipation inside the part during inrush can be calculated as:

For the given power dissipation, the thermal shutdown time of the device must be greater than the ramp-up time t_R to avoid start-up failure. Figure 9-3 shows the thermal shutdown limit. For 1.69 W of power, the shutdown time is more than 10 s, which is very large as compared to t_R = 20 ms. Therefore, it is safe to use 20 ms as the start-up time for this application.