What about using a USB power switch to limit in-rush and current limit any USB devices? Like the dual AP2142A http://www.diodes.com/datasheets/AP2142A_52A.pdf
Cheers, Ed. Date: Mon, 14 Nov 2011 12:15:38 +0800 From: [email protected] To: [email protected] Subject: Re: [Milkymist-devel] reset circuit vs. USB inrush current This means that a reset circuit operating from the only externally regulated 5 V input with a 4.4 V threshold voltage is likely to experience resets when connecting USB devices. The current reset IC you're using is APX803-44SAG, right?http://www.diodes.com/datasheets/APX803.pdf Its reset threshold: min. 4.31V typ. 4.38V max. 4.45VIf using a 4.0V APX803-40SAG, then becomesmin. 3.94V typ. 4.00V max. 4.06V If we stick with the idea of monitoring only a single input, which would then have to be the 5 V rail, I would recommend using a reset chip with a threshold voltage of 4.0 V. This will still let the regulator of the 3.3 V rail produce a 3.0 V output under worst-case conditions, while providing a safety margin for USB devices with high inrush current and for power supplies providing a low "5 V" voltage. These experiments should be confirmed with other power supplies, including an official M1 power supply. yes, needs to be confirmed when replacing a 4.0V one later.-Adam _______________________________________________ http://lists.milkymist.org/listinfo.cgi/devel-milkymist.org IRC: #milkymist@Freenode
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