When the switch is enabled, the output capacitors must be charged up from 0 V to the set value (3.3 V in this example). This charge arrives in the form of inrush current. Inrush current can be calculated using Equation 1.

where

• C is the output capacitance
• dV is the output voltage
• dt is the rise time

The TPS22976 offers adjustable rise time for VOUT. This feature allows the user to control the inrush current during turnon. The appropriate rise time can be calculated using Table 9-1 and the inrush current equation. See Equation 2 and Equation 3.

To ensure an inrush current of less than 400 mA, choose a CT value that yields a rise time of more than 181.5 μs. See the oscilloscope captures in the Application Curves section for an example of how the CT capacitor can be used to reduce inrush current.