Hey Charliem_1216-
Thanks for the information. I'm using the 2.4 kernel, so I don't know the
overcurrent condition in the syslog.
Regarding one or two ports, I see that the USB power on the TS-7260 schematic
is just wired to both of the 5V power pins on the connector, so I don't think I
get any more power by using two connectors.
I don't really have space in the design to fit a USB hub in between the
devices. Additionally, I'm not sure I like the reliability of using an extra
device in there. This application is part of an autonomous instrument that is
deployed for a year at a time.
Do you know if the 2.6 startup behavior might not turn on USB power until the
drivers are in place?
--- In "charliem_1216" <> wrote:
>
> --- In "wrsimpson.alaska" <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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