Steve Wiseman wrote:
> While thoroughly violating the USB spec, I've started powering my B3 from
> my PC's USB port (nominally 5V, IIRC, the USB standard permits 4.5-5.5V).
> The red Reset light glows dimly when I do this, since the LED's pulled up
> to VRaw, rather than 3V, but the board works just fine.
> The schematic states 4.6Vmax on VRaw (which turns into VBatt). I can't
> remember why, for the life of me. The MAX1586 (Xscale power) claims to be
> OK up to 5.5V, and the TPS75003 (FPGA power)is good to 6.5V. Is this a
> hangover from an earlier design iteration, or a real limit? (being able to
> be USB powered has a certain simple charm - I'm now running with a 1N4001
> in series with the PSU, to stop the red glow and reduce the damage a
> backwards-power blunder would cause...
This is something we know about - the nastiness is just cos a couple of
power control (or is it reset?) lines are pulled up to VDD_RAW but
really want to be 3.3V. I believe that the respin has acquired an LDO to
sort this out and thus make 5V nice.
Chris
--
Chris Jones -
chris@martin-jones.com
Martin-Jones Technology Ltd, makers of Solidlights
148 Catharine Street, Cambridge, CB1 3AR, UK
Phone +44 (0) 1223 655611 Fax +44 (0) 870 112 3908
http://www.solidlights.co.uk/
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