Hi Notaz,
Am 12.09.2014 um 18:42 schrieb Grazvydas Ignotas notasas@gmail.com:
On Fri, Sep 12, 2014 at 5:59 PM, Michael Mrozek mrozek@openpandora.org wrote:
Am Fri, 12 Sep 2014 16:58:06 +0300 hat Grazvydas Ignotas notasas@gmail.com geschrieben:
Hi,
Later it was found that overcurrent protection doesn't actually work. I'm not sure if it was ever fixed..
I think so, the Rebirth Pandora had extra protection stuff added to the USB port. With CC Pandoras, you could even get a small electrical shock from the USB Port (and fry the Port with that), but that doesn't happen anymore on the later Pandoras.
I really hope it will all work properly this time..
We need to check that upfront, now we know what to look for, which helps.
that is what I am doing with the stress-tests.
We use a TPS2505 "INTEGRATED DUAL USB SWITCHES, BOOST CONVERTER AND LDO" which is designed for that purpose.
It has • Adjustable Independent USB Current Limit – 100 mA to 1100 mA • 5.1-V, 1100-mA boost converter, a 200-mA, 3.3-V LDO linear regulator and dual USB 2.0 compliant power outputs with independent output switch enable, current limit, and over-current fault reporting.
I have just checked that the resistors which control the current limit are chosen more for 500 mA. If I remember this correctly it comes from some reference design.
So I will simply choose a different resistor value so that we can draw 1 A from each of the USB ports (but not more than 1.1A in total). Then of course there might be a different limit - if the battery and DC/DC converter can provide enough energy/current at 3.3V battery voltage…
That is something we have to find out with the next prototype.
• FTDI232 (Linux console)
responds on the USB side.
Again, I hope it doesn't waste power..
It shouldn't. At least on the EVM it gets it's power from the PC. As soon as you connect it to your PC (without connecting the EVM to any power source), the small LED lights up on the EVM and the PC finds the USB to Serial adaptor.
We have the same on the Pyra mainboard (except the LED). The FTDI is powered by the host cable and does not draw any energy from the battery.
That LED doesn't guarantee that there is no leakage current of some sorts going from OMAP to the chip while the chip is unpowered from the USB side (which will be most common state).
No, but there is a TXB0102 level shifter which protects against this issue (no external power to the FTDI but OMAP powered up).
BR, Nikolaus