GTA02 voltage chart

[Werner Almesberger]

Since the voltage levels at which various things happen are getting a
bit confusing, here's a quick overview:


Voltage Where   What happens
 
 4.5 V  USB     USB voltage required for battery charging
        USB     Minimum USB voltage at device guaranteed by USB 2.0
 4.2 V  BAT     Battery float voltage (NoPower default and u-boot setting)
 3.6 V  USB     +/- 0.35V, USB adapter present (rising)
 3.5 V  USB     +/- 0.35V, USB adapter present (falling)
 3.4 V  BAT     u-boot wait_for_power threshold
 3.1 V  SYS     Minimum SYS voltage, interrupt and timeout (set by u-boot)
        BAT     Battery threshold (NoPower default)
 3.0 V  SYS     Minimum SYS voltage, interrupt and timeout (NoPower default)
 2.85V  BAT     Battery conditioning (NoPower default)
 2.8 V  BAT     Battery threshold (set by u-boot)
 2.7 V  BAT     Battery conditioning (set by u-boot)
 2.5 V  SYS     SYS voltage for immediate shutdown into Save mode
 2.4 V  BAT     GTA02 battery cuts off
 2.2 V  BAT     GTA01 battery cuts off
 2.0 V  SYS     +/- 0.3V, SYS voltage to enter Save/NoPower
 1.3 V  BUB     +/- 0.3V, Backup battery present threshold
 0.0 V  BAT     No battery or battery in cut-off


NoPower default means that the PMU sets this value if without any power,
i.e., no mai battery, no USB, and the backup battery is below 1.3V. If
SYs remains at at least 2.0V or the backup battery is above 1.3V, the
PMU will remember the previous settings.

u-boot changes some of the PMU settings during early initialization.

The SYS voltage is basically max(USB, BAT) and all the PMU's regulators
are supplied from it.

- Werner