On Fri, 10 Feb 2012 14:50:05 -0800, "Scott W" <
Scott...@gmail.com>
put finger to keyboard and composed:
>Mine plugs directly from the DC cord & it is a flat connector, not USB. That
>is how I deliver power to the unit. The true USB port is only used when I
>connect it to a computer. I have mine mounted on my motorcycle, bypassing
>the stand it came with.
AIUI, the GPS can be powered and charged either via the side mini-USB
connector or via the rear DC power socket (wherever that is).
If an adapter, either AC or DC, is plugged into the rear, then the
unit buzzes. OTOH, if the mini-USB connector is used, then there is no
buzzing. This suggests to me that, if two power sources are connected
to the unit at the same time, then the side port takes precedence. It
probably disables the rear port, which would explain why the buzzing
goes away.
One thing still bothers me, though. The OP states that the AC adapter
plugs into the rear port, yet you are saying that this is not a USB
port. The guide, OTOH, refers to the AC adapter as a standard
inclusion with the nuvi 350, so presumably it has a micro-USB plug
(???).
One other thing that may be worth considering is the current draw. A
computer's USB 2.0 port is current limited to 500mA, so this would
place a limit on the charging current via the side port, at least when
the GPS senses a USB host controller. AIUI, USB OTG (on the go)
specifies a signalling system that enables a device to draw a greater
current when it senses a charger. Maybe that could account for the
difference in behaviour.