USB ports on battery

[zokl]

Is it possible to use usb ports or usb hub if the olimex boards goes on battery?

I have tried it but the board goes off in 30 s after unplugging the power. I had in usb ports two cameras or USB hub.

I am using debian distribution.

[JohnS]

USB is & needs 5V, so I don't see it working unless you provide 5V.

John

[zokl]

USB is & needs 5V, so I don't see it working unless you provide 5V.

John

If i use olimex a20 board and 15" display which is supplied from olimex boards it works. If i put one usb camera to usb port it works too. If i put ther the other it works about 30s and then poweroff. The same beheviour is with usb hub with its own power supply adapter. 30 second from battery and then off without some information in console. The power consuption of usb camera is about 100 mA. The usb hub has 150 mA. My battery is 3000 mAh. If i use hub without external power supply the system goes off in 3 s.

Maybe is there some voltage or current orotection which shut the system down. I try to change some values in pmu section in script.bin but without success.

Is it possible to power the usb devices from olimex internal battery?

[dave-at-axon]

This is very similar to the issue I am seeing when I power up a STEP UP supply on the 5V rail.

The USB will work on battery as long as the current consumption or spikes does not cause the 3.3V rail to drop too low as this causes the system to shutdown.

The system has a boost supply that generates the 5V (USB power) from 3.3V but the 3.3V supply is only generated from a buck regulator (STEP DOWN) so if the battery drops below 3.3V the system will shut down.

I can run a GPRS modem and WiFi dongle on battery and they work well. It's all about the surge that your USB device might take. The 3.3V supply on the A20 is the culprit. I know this as I have tested this with a scope and can see the voltage drop on the battery input. I had a design a few years ago that used a BUCK/BOOST supply so it would work with anything from 2.5V to 5V and generate 3.3V output. That design worked with the same STEP UP supply I am trying to use with the Olimex board.

The next revision of the A20 needs this 3.3V section changed to use a BUCK/BOOST regulator instead.

[jess]

I can run a GPRS modem and WiFi dongle on battery and they work well. It's all about the surge that your USB device might take.

I'm just curious how big were the surges measured by you during the GPRS transmission time (as from what I read so far they might be over 2A for 50ms) ?

[dave-at-axon]

I am not seeing any drop on the 5V supply when GPRS is transmitting data. The designer of the modem has to take care that the on-board supply can handle the drops.

For my own GPRS modem boards, I have enough storage capacitance to handle these current peaks so that the supply itself to the modem is not compromised.