Dual-voltage regulator meets USB-power needs

摘要

This design idea stems from the limited availability of IC voltage regulators that can meet key USB-power specs, coupled with the need for turn-on sequencing and rise-time control at each output. As always, for PC-related designs, minimum cost is a primary motivation. USB specs require all loads to limit inrush cur-rent to less than 100 mA plus 50 μC of charge when powered on. If permission is granted to increase the load to 500 mA, inrush limiting may be required again to prevent excursions over the 500-mA limit.