A normal USB port supplies 100mA @5V but I need more. Most ports happily give 500mA but to do it right you have to inform the USB host first. My device (a RFM12B Wireless to Ethernet Bridge) should be able to operate from the following power sources:
* USB when connected to a computer (mostly for debug and firmware uploading)
* USB when connected to USB power supply (for production)
* External DC jack (for production, may be removed in favor of an USB power supply)
* Internal LiPo battery
The internal LiPo battery is charged using a MAX1555 which takes 90mA from USB or 280mA from the DC jack. There is also a cap (0.22F, 3.6V) which powers the RTC for a few days or so. The LiPo is completely optional so I do need the additional cap.
So about 1.5W should be enough to power my device which is still below (500mA*5V=2.5W) an USB port will provide. I've chosen an external 3.3V regulator which is able to provide the required 3.3V current.
Is there any chance to modify the USB chip on the Teensy to request 500mA from the host?
If I do understand it correctly USB chargers will always supply 500mA and don't listen to the USB device. As many of these USB chargers supply much more than 500mA it may even be possible to connect these devices to the MAX1555 DC input. But how is it possible to detect such chargers?
many thanks,
Thomas
* USB when connected to a computer (mostly for debug and firmware uploading)
* USB when connected to USB power supply (for production)
* External DC jack (for production, may be removed in favor of an USB power supply)
* Internal LiPo battery
The internal LiPo battery is charged using a MAX1555 which takes 90mA from USB or 280mA from the DC jack. There is also a cap (0.22F, 3.6V) which powers the RTC for a few days or so. The LiPo is completely optional so I do need the additional cap.
Code:
My current power budget:
Teensy3 + Wiz820io + RFM12B: 0.8W (3.3V)
Supercap charging (max): 0.25W (3.3V)
LiPo Charging (max): 0.3W (5V)
So about 1.5W should be enough to power my device which is still below (500mA*5V=2.5W) an USB port will provide. I've chosen an external 3.3V regulator which is able to provide the required 3.3V current.
Is there any chance to modify the USB chip on the Teensy to request 500mA from the host?
If I do understand it correctly USB chargers will always supply 500mA and don't listen to the USB device. As many of these USB chargers supply much more than 500mA it may even be possible to connect these devices to the MAX1555 DC input. But how is it possible to detect such chargers?
many thanks,
Thomas