Neo 1973 Battery Charging Logic
The PCF50606 supports a variety of Neo1973 Battery charging modes, based around the hardware limitations of USB.
Some USB hubs only provide up to 100mA per device. If more than the available current is drawn from them, they may be reset, or power off. This resets all devices connected to the USB bus, possibly causing data loss. So, fast charge mode is only enabled after the Neo is told that it is safe to charge at this current.
An alternative method is used when connected to a more USB-compliant dumb charger. If the Neo measures 48 kΩ +/- 1% between usb pin 5 and ground, it will detect the dumb charger and use it for fast charging.
|WARNING: While we have spent a significant amount on various safe-guards such as battery-internal overcurrent/overvoltage protection, manual twisting with low-level charger control aspects is not recommended. It might damage either the battery or charging circuit.|
The default mode is what the PMU calls 'Pre Charge'. In which we draw up to 100mA charging current from the USB socket. This mode is safe to use on any USB socket, since the USB specification mandates that 100mA is always available.
However, 100mA charging at a 1200mAh Neo1973 Battery means around 12hrs charging time, not very practical at all.
Fast Charge is what the PMU calls the charging mode in which we draw up to 500mA charging current from the USB socket. This mode can only be used if the USB stack on the host controller has selected a USB Configuration for the Neo which allows it to draw 500mA.
By default, if you apply +5V to the USB device socket, we draw only 100mA.
Fast Charge (CCCV)
Fast charging, using first constant current, later constant voltage. This is what we use for our Li-Ion Neo1973 Battery
Fast Charge (CVCC)
Neo1973 emergency charging
from deep discharged battery
A deep discharged battery is one where the terminal voltage is below the minimal voltage threshold. The Neo1973 (specifically: The PCF50606 PMU) will not power-on the device. see also Neo1973 GTA01 Power Management
If you make sure to remove the USB cable and put a deep discharged battery into the Neo1973, the battery can still be charged. All you need to do is to provide 5V to the USB socket, by either connecting the Neo1973 to some USB port or a dumb USB charger.
The battery will charge only with 100mA, and it will take a couple of hours until the battery is again charged to a level where it can power the phone.
| NOTE: Please do not press the power button before you have waited for something like four hours. If you do so, the phone might [partially] power up, and draw more power than the 100mA supplied by the charger/USB, and so begin discharging itself again.
If you did press the power button,
The procedure to follow is:
- Open Case.
- Remove Battery.
- Wait 20s. This resets the hardware, and makes sure nothing is drawing current during the next stage.
- Insert the Battery.
- Plug into a USB host, or USB charger. At this time, the battery will be charging at a low rate.
- Wait 1 hour. At this time, the battery will be approximately 5% charged, which should run the Neo for several minutes. This time needs to be resolved: it is not quite clear how long to charge a deeply discharged battery before the device is able to request a 500 mA fast charge current.
- If you have a USB host, plug it into a port capable of sourcing 500mA and load the appropriate drivers, so the neo can negotiate to draw 500mA.
- If you have a dumb charger, see the Bootloader page for how to add a u-boot menu entry to turn on fast-charging.
Proposals for alternative charging schemes
An alternate method - for example sensing if there is no USB communication from the host for 30 seconds - as may be the case with dumb 'USB chargers' - would need to be used to be compatible with the vast majority of already existing hardware. This has a small risk of causing buses it is connected to in suspend mode, when they are not active, to crash, and is not compliant with the specification.
- The USB spec requires the host to reply in a much shorter time than 30 seconds. Waiting that long is overkill and would be very annoying if you were trying to charge with something like a crank charger.