[Trac #813] Power-up failure due to USB current draw

[Zarro Boogs per Child]

#813: Power-up failure due to USB current draw
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 Reporter:  dwmw2     |       Owner:  mlj    
     Type:  defect    |      Status:  new    
 Priority:  blocker   |   Milestone:  BTest-3
Component:  hardware  |    Keywords:         
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 Switching the USB 5V power on causes a direct short through the two 100µF
 capacitors and draws so much current that the AC input shuts down.

 Q2B33 firmware attempts to alleviate this by staggering the switches so
 that we only charge one of the caps at a time, which seems to be
 sufficient for now.

 For B3 we need a better solution -- potential solutions include:
  - increase total power input rating
  - increase capacitance on Vin to cope with the surge in demand
  - use a soft-start power switch for the USB 5v rail.

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Ticket URL: <http://dev.laptop.org/ticket/813>
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