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Understanding SWIFT Step-Down DC-DC Converters Slide 10

Heavy load requirements during start-up and/or fast initial charging of bypass capacitors may result in a surge current. For example, when a power supply is charging up processor bypass capacitors, the load can look like a short circuit as the capacitors charge up. This results is an inrush current spike, shown as Iss. If the current spike is too high as shown with Ipk, the current limit of the power supply may trip and cause the power supply to limit the current or the power supply may shut down and restart, depending on the current limit technique implemented by the DC/DC converter. The worst case situation is that another component of the power supply overstresses due to the excessive current flow. To solve this problem, the power supply can be oversized to accommodate the inrush current level, or a SWIFT DC/DC converter with an adjustable soft-start can be implemented to slow down the charging of the bypass capacitors, as shown in the waveform rising to Vcore.

PTM Published on: 2011-11-10