USB-power Dual-voltage regulator


Posted on Dec 26, 2012

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 current 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.



The other troublesome USB-power requirement is the "suspend"-current maximum of 500 µA, of which you may use only 250 µA; a termination resistor requires the rest. Suspend requires the load to power down but keep alive just enough to liste




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