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USB Li-Ion Charger

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chinzei
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RE: USB Li-Ion Charger 2008/10/24 20:39:32 (permalink)
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When a hub concerns to the high-/low-power enumeration, the stuff becomes much complicated.

Bus-powered hub can supply only 100mA (one unit load) / port, but self-powered hub may provide 500mA / port. so far, so good.

The current power status of hub (bus-/self-powerd) is reported by Get_Status(DEVICE) - self powered field.

Problems:
- Many hubs on the market always report itself as a self-powered device, even when being used as a bus-powered device.

- On hub enumeration, OS should examine current power status of the hub.

11.13 Hub Configuration (usb_20.pdf p340)

However, Windows XP SP2 and original Vista don't issue any Get_Status(DEVICE) on hub enumeration.
This problem was fixed on XP SP3 and Vista SP1.

Tsuneo
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chinzei
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Re:USB Li-Ion Charger 2011/02/08 13:02:29 (permalink)
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Aha, sorry
I posted to a wrong thread.
This post should go to
http://www.microchip.com/forums/m555918.aspx




Here are similar discussions,
http://www.microchip.com/forums/m404231.aspx
http://www.microchip.com/forums/m375994.aspx

IMHO, the effort to implement swapped configurations is unrewarded.
In most cases, single config of 500 mA will do. 

The reasons are,
1) The current draw is limited to 100mA, just when your device is connected to a bus-powered hub.
2) Many hubs on the market always report its status in self-powered, even when it is actually in bus-powered.

500 mA config is not enumerated when the bus-powered hub reports its status correctly.
OS puts a warning dialog for insufficient power supply.
Therefore, you should have a warning on the manual, "When you see power supply warning, connect this device directly to the PC USB port, or over a self-powered hub". Smile

Rather, you had better to have a VBUS voltage monitor, and a power-down circuit on your device.

Tsuneo
post edited by chinzei - 2011/02/08 13:07:48
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