Hi,
> > 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 fact that USB switch does protect 5V(J21/J3) rail at the beginning, While analyzing results of README, probably need to include/think another circuit composed by F2 MINISMDC200F-2 2.0A and D14/D15 5.6V When usb switch reached short-current condition, the F2 must also try to trip firstly then recover its positive resistance and arise back normally up 4.6V within 40 ~ 50 us. This reality is decided now by PTC fuse-oriented. One thing, the "Input" noticed that from your lab supply should be regarding as a real output voltage of the official adapter with 2.5m cable: see, http://en.qi-hardware.com/wiki/File:Sharism_5V_2000mA_KS032940_s54878.pdf The 5V/2A adapter is designed internally and pulled up to fine tuned with cable loss(drop). fyi. So maybe you can tune highly a bit on the lab supply's voltage as the "Input" column for real application. - adam
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