The USB specification requires that it will operate between 4.5 and 5.5 Volts.
For the 5 Volt power jack, the PMIC will operate between 4.5 and 5.5 Volts.
BUT, the PMIC will shut down and go into self protection above or below
those Voltages. So, in order to allow for some noise and Voltage spikes,
so that you have margin against the shut down points, I recommend that
you operate the Power Jack and USB between 4.75 and 5.25 Volts.
Physical damage will not occur until at least 7 Volts, but it will self protect
(turn itself off) starting at 5.50 Volts
If you question has to do with running the BBB from batteries, I suggest that
you have an external boost/buck converter, so that the power to the
BBB stays at a safe and comfortable 4.75 to 5.25 Volts, no matter what the
battery is doing.
--- Graham
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