I did some testing of the current-limiting USB switch we're considering for M1rc4. In this round of tests, I supplied the M1 from a lab power supply (which means that current limits are strictly enforced) and switched resistive loads on one USB port with labsw. The latter simulates hot-plugging.
Details are here: http://projects.qi-hardware.com/index.php/p/wernermisc/source/tree/master/m1rc3/usbpwr/README Key findings: - if my M1pre-rc4 is operating at or slightly below the nominal supply voltage, the USB switch does not protect the 5 V rail from deep drops in the case of shorts ("0 Ohm") http://projects.qi-hardware.com/index.php/p/wernermisc/source/tree/master/m1rc3/usbpwr/usb-short-10us.png - in the same configuration, a 2 Ohm load causes almost no visible upset: http://projects.qi-hardware.com/index.php/p/wernermisc/source/tree/master/m1rc3/usbpwr/usb-2R-200us.png - if increasing the supply voltage above the nominal 5.0 V, also "zero-Ohm" upsets are survivable: http://projects.qi-hardware.com/index.php/p/wernermisc/source/tree/master/m1rc3/usbpwr/usb-short-5V4.png I'm not quite sure yet why the USB voltage (channel 2) doesn't drop to zero when shorted. Might be a grounding problem. - Werner _______________________________________________ http://lists.milkymist.org/listinfo.cgi/devel-milkymist.org IRC: #milkymist@Freenode
