N900 Hardware Battery Charger
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The battery charger is the [http://focus.ti.com/docs/prod/folders/print/bq24150.html bq24150] charger from TI. | The battery charger is the [http://focus.ti.com/docs/prod/folders/print/bq24150.html bq24150] charger from TI. | ||
| - | It features reverse boost mode - which enables power to be supplied to a USB device connected to the N900. | + | It features reverse boost mode - which enables power of up to 200mA@5V to be supplied to a USB device connected to the N900. |
When initially powered on, this chip, and the [[N900 Hardware USB PHY|USB interface]] chip enable charging from dead without any software running. | When initially powered on, this chip, and the [[N900 Hardware USB PHY|USB interface]] chip enable charging from dead without any software running. | ||
Revision as of 11:43, 13 December 2010
The battery charger charges the battery, and supplies power when running connected to USB. It can also supply power for USB Host mode.
Hardware
The battery charger is the bq24150 charger from TI.
It features reverse boost mode - which enables power of up to 200mA@5V to be supplied to a USB device connected to the N900.
When initially powered on, this chip, and the USB interface chip enable charging from dead without any software running. This mode of charging respects the maximum current available without negotiation - 100mA in the case of a normal USB connection, or 1.2A in the case the charger is plugged in.
It also properly supports charging very depleted batteries gently.
There are safety implications of software drivers for this chip, the chip can be configured to have an output voltage of up to 4.44V, which is higher than the absolute maximum voltage of 4.2V that li-ion batteries can be safely charged to.
Software
There is no kernel driver for this chip - it is driven over I2C by BME. BME (Battery Managment Entity) needs replaced with an open-source version in order to allow easy operation in USB host mode.