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From Wiki:
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$ c" ?2 T( p) x, B% s8 WUSB supplies bus power across VBUS and GND at a nominal voltage 5 V ± 5%, at supply, to power USB devices. # _# \& t" m# K; b4 v$ |; f( S6 ~
Power is sourced solely from upstream devices or hosts, and is consumed solely by downstream devices.
9 j& o4 h" ~' RUSB provides for various voltage drops and losses in providing bus power.
?: L0 R5 ^+ {( o% uAs such, the voltage at the hub port is specified to be in the range 5.00 +0.25 / −0.60 V by USB 2.0, and 5.00 +0.25 / −0.55 V by USB 3.0. " n7 o% S, L; N, `' P( X
5 D6 @3 g3 z8 a2 K! zNormal USB port:6 ^1 ]8 c) B7 \' M, u
5.0 +0.25 / -0.25 V6 Z6 Y( P6 x5 T) W
6 D7 ?/ i/ Y Y+ L. aHub port:
+ [6 M- t8 ^2 [' eUSB 2.0: 5.0 +0.25 / -0.6 V) `+ Z, b6 A5 O/ k) g
USB 3.0: 5.0 +0.25 / -0.55 V |
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