--- In "wrsimpson.alaska" <> wrote:
>
> We are using a TS-7260 SBC to control an Ocean Optics spectrometer (a
> MayaPro) and are having problems with the USB system. The problem has to do
> with the fact that the MayaPro consumes very near the USB limit of 500mA. It
> appears to exceed significantly (>600mA) during power-on of the USB device.
>
> The first problem I had was that the internal 5V charge pump cannot deliver
> this much current. I solved this by plugging the TS-7260 into a regulated 5V
> supply and inserting JP7, which then directly puts the regulated 5V to the
> USB power. This helped a lot, but didn't solve the full problem.
>
> Now, I see the USB device in two different power states. When plugging in
> the device or turning on the computer, I sometimes see one or the other
> state. One is the "normal" working state, where it draws 470mA and has a
> voltage across the USB nominal 5V of 4.6V. I think the voltage drop is
> partially on cables, contacts, and possibly the MIC2026 chip on the TS-7260.
> The other power state is "high current", where the USB device draws 690mA,
> but only has 2.7V voltage across the nominal 5V. I believe the other 2.2V is
> dropped in the MIC2026 chip because that chip becomes very hot in this state.
> From looking at the MIC2026 data sheet, I believe that it has gone into
> overcurrent or thermal shutdown, which should only happen at 1000mA. It
> might be that the USB device spiked that high, but I don't know.
Isn't that 500 mA per port?
>
> Another funny observation is that when I start with the TS-7260 off and the
> USB device plugged in, here's what see upon power up. The TS-7260 starts to
> boot, and the current of the USB device goes in the high-current state. The
> MIC2026 gets very hot. The TS-7260 boots fully into runlevel 3, and then
> when I load the USB modules, the USB device suddenly switches into its
> operational state (normal current). The thing that fixes the system is the
> loading of the module "insmod usb-ohci-ep93xx". The current goes normal
> right after loading this module. I have no clue what is happening here.
> Possibly that module momentarily interrupts the USB power and resets the USB
> device? Possibly the USB device is drawing a high current before it
> enumerates onto the USB system?
You don't say which kernel you are using, 2.6 or 2.4. After 2.6.10, the USB
initialization method changed substantially. Don't know about 2.4, but in 2.6
overcurrent conditions should be in the syslog.
>
> My question is if anybody has seen this problem before, and figured out a
> workaround.
No, not myself. I do have a couple of drive enclosures that use two USB ports:
one power & communication, and a second for power only. Perhaps that would be
an option for you if you're running into a per-port overcurrent. Another
option would be to use a powered USB hub between the TS-7260 and your
spectrometer if you have space, and room in your power budget. You may still
need to use two connectors.
regards, ......... Charlie
>
> Thanks!
>
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