The TPS4022 device supports several soft-start times between 600 μs and 9 ms. Use the TON_RISE PMBus command to select the soft-start time. See the Section 8.6.1.19 command description for full details on the levels and implementation. When selecting the soft-start time, carefully consider the charging current for the output capacitors. In some applications (for example, those with large amounts of output capacitance) this current level can lead to problems with nuisance tripping of the overcurrent protection circuitry. To ensure that this does not happen, include a consideration of the output capacitor charging current when choosing the overcurrent threshold setting. Use Equation 6 to calculate the output capacitor charging current.

Equation 6.

where

• I_CAP is the startup charging current of the output capacitance in A
• V_OUT is the output voltage of the converter in V
• C_OUT is the total output capacitance in F
• t_SS is the selected soft-start time in seconds

After calculating the charging current, the overcurrent threshold can then be calibrated to the sum of the maximum load current and the output capacitor charging current plus some margin. The amount of margin required depends on the individual application, but 25% is a suggested starting point. Individual applications may require more or less than 25%.