A capacitor at the SS_TR pin is utilized in order to slow the rise of the internal reference voltage, V_{REF(internal)}. By slowing the rise of the reference voltage during startup, the output voltage slew rate will be controlled. This is useful to prevent excessive inrush current.

Measured soft start time for the SS_TR voltage to rise from 10% to 90% of its value are detailed in the Electrical Characteristics. Generally a 22nF or larger ceramic C_SS capacitor is recommended; however, values down to 5.6nF are shown if a faster startup is desired. Additionally, Equation 7 can be used to approximate startup equations for arbitrary capacitor values.

where

• t_SS in ms
• C_SS in nF

Note that the SS_TR pin follows that of an RC charging circuit curve. Therefore, the output voltage follows a similar curve.

When any of the following scenarios occur, the SS_TR pin is discharged through the internal R_{SS(discharge)} pull-down resistor (typically 442Ω):

• the input UVLO is triggered,
• the EN pin is pulled below V_EN(falling) (0.51V typical)
• the FAULT pin is pulled above V_{FAULT(rising)} (0.6V typical)
• the COMP pin reaches the COMP_SHDN threshold (1.9V typical)
• a thermal shutdown event occurs

When the SS_TR pin is discharged, the device cannot restart again until it has discharged to below SS_startup (typically 20mV) in order to ensure proper soft-start behavior.