Backup Battery; Normal And Extreme Voltages - Nokia N900 Service Manual

RX-51
System Module
Figure 49 Charging circuitry
USB charging circuit BQ24150 starts charging with 100mA immediately after USB cable is connected. ISP1707
can control charging current to 500mA if a wall charger is detected. RBG LED indicates charging.
When Gaia wake up level is reached it wakes up OMAP3 and detects used charger immediately. During this,
CellMo is kept to reset state. If a wall charger is detected a device can be booted immediately, otherwise a
battery is charged in low power mode until a bootable level is reached.
If a USB cable is connected before a battery, charging is not started. The USB cable and battery must then be
removed before charging is started.
A device starts charging with 100mA if a battery level is under 3.5V but a cold flashing is prevented with low
battery, this ensures that there are no reset loops. Rom code has a 3 sec timeout for USB enumeration.

Backup battery

When the main battery is not attached, APE side EM ASIC goes in backup mode using back-up battery that
supplies voltage to RTC in EM ASIC. CMT side does not have its own backup battery.

Normal and extreme voltages

Energy management is mainly handled by the APE side EM ASIC called Gaia. It supplies most of the power
supplies on APE side together with few external regulators. CMT side energy management is handled by
Gazoo EM ASIC. It powers the CMT processor, cellular RF, SIM card and GPS.
In the table below normal and extreme voltages are shown when a BL-5J battery is used.
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