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...
Steve
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