Fujitsu stylistic lt, Reference Manual

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6-1
Chapter 6
System Power
This chapter covers the Stylistic LT pen tablet’s system power hardware, power management states, and
state transitions.
System Power Hardware 6
The Stylistic LT pen tablet uses components designed for low power consumption in mobile applications.
DC power, whether supplied by the battery pack or an external source, is regulated to different voltage
levels required to power various components in the system.
Battery Pack 6
When the system is not connected to external power, system power is provided by the battery pack.
When an external DC power source is connected to the pen tablet, the battery pack is charged and the
system is powered by the external source.
The battery pack can be removed from the pen tablet and charged in an external charger. When removing
the battery pack, be sure the system is first suspended-to-disk or attached to DC power; failure to do so
could result in loss of data.
The pen tablet is equipped with a microcontroller, called the power management microcontroller unit
(PMU), which is dedicated to managing battery pack power. The battery pack charge is monitored by the
PMU. The PMU determines the percent of charge remaining in the battery pack and supplies battery
status information to the system through a dedicated interface.
A low voltage level detect circuit (independent of the PMU) measures the battery pack voltage level to
determine whether the battery pack voltage has dropped to the critically low level (the critically low
voltage varies depending on total current draw). When the system is running and the critically low
voltage level is reached, the circuit forces the system into Suspend mode and the Power icon indicates the
critically low condition.
When the system is forced into Suspend mode by a critically low battery, the system is powered by the
remaining charge in the battery pack. In this mode, the Suspend/Resume button is disabled and system
operation cannot be resumed until either an external DC power source is connected or a battery pack
with adequate charge is installed. See “Battery Charge Level and Power Management” on page 6-10 for
details on system activity for different battery charge levels.